Strategic application of convective cooling to maximize the thermal gradient and reduce heat stress response in dairy cows.

This study determined the effectiveness of convective cooling at different times of day when air temperature (Ta) was cycled from day to night. Mid-lactation Holstein cows (n = 12) were placed in 3 environmental chambers (4 cows per chamber) and acclimated to Ta 19.9°C (thermoneutral; TN) for 7 d followed by an incremental increase over 3 d to a heat stress (HS) condition. Conditions were maintained for 11 d at high and low daily Ta of 33 and 23°C, respectively. To determine adaptive HS response, the HS period was divided into early (E: d 11 to 14) and late (L: d 17 to 20) periods. During HS, cows were exposed to continuous fan (convective) cooling (CC), 8-h day fan cooling (1100 to 1900 h; DC), or 8-h night fan cooling (2300 to 0700 h; NC). Compared with DC, the NC treatment maximized the thermal gradient during the convective cooling. Each animal received all treatments within 3 trials using a repeated 3 × 3 Latin square design. Cows were fed a total mixed ration and milked twice daily. Thermal status was assessed by using thermal conductance and average daily values for mean, minimum, and maximum rectal temperature (Tre), skin temperatures, and respiration rate. Percent reduction in dry matter intake from TN to HS was less for CC than DC and NC, with no change from E to L periods. The DC group exhibited the greatest trend for a percent reduction in total milk yield below CC due to the significantly lower morning milk production. All values for total daily milk production decreased from E to L periods, with E to L reductions in both morning and afternoon milk production. Minimum Tre for CC and NC cows was 0.4°C below DC. In contrast, maximum Tre was similar for NC and DC groups, at 0.5 to 0.6°C above the CC group. Skin temperature for CC cows was always less than DC cows. Skin temperature for NC cows was equal to CC for minimum skin temperature, but exceeded both CC and DC cows for maximum skin temperature. Average skin temperature decreased from E to L, which suggested heat adaptation. The thermal advantage of night (lowest Ta and greatest thermal gradient) versus day cooling (greatest Ta and lowest thermal gradient) was increased heat transfer via thermal conductance with NC. The higher thermal strain of DC cows caused a larger percent decrease in morning milk yield than for NC cows. In contrast, use of convective cooling at night in the absence of elevated humidity could sufficiently reduce heat strain beyond DC to maintain milk production at a level that is closer to that of CC cows.

Molecular characterization of non-aureus Staphylococcus spp. from heifer intramammary infections and body sites.

The purpose of this study was to investigate non-aureus Staphylococcus spp. intramammary infections (IMI) in periparturient heifers and determine the relationship of precalving body site isolation with precalving IMI and postcalving IMI using molecular speciation and strain-typing methods. Primiparous heifers were enrolled at approximately 14 d before expected calving date. Precalving mammary quarter secretions and body site swabbing samples (teat skin, inguinal skin, muzzle, and perineum) were collected. Postcalving, mammary quarter milk samples were collected for culture and somatic cell counting. Precalving body site samples were cultured, and up to 10 staphylococcal colonies were saved for characterization. Staphylococcal isolates were speciated using matrix-assisted laser/desorption ionization time-of-flight mass spectrometry or sequencing of rpoB or tuf. Pulsed-field gel electrophoresis was used to strain type a subset of isolates. Overall, Staphylococcus chromogenes, Staphylococcus agnetis, and Staphylococcus simulans were the most common species identified in precalving mammary secretions, whereas S. chromogenes, Staphylococcus xylosus, and S. agnetis were the most common species found in postcalving milk samples. The most common species identified from body site samples were S. chromogenes, S. xylosus, and Staphylococcus haemolyticus. Mammary quarters that had a precalving mammary secretion that was culture positive for S. agnetis, S. chromogenes, or Staphylococcus devriesei had increased odds of having an IMI with the same species postcalving. A S. chromogenes IMI postcalving was associated with higher somatic cell count when compared with postcalving culture-negative quarters. Among heifers identified with a non-aureus Staphylococcus spp. IMI either precalving or postcalving, heifers that had S. agnetis or S. chromogenes isolated from their teat skin had increased odds of having the same species found in their precalving mammary secretions, and heifers with S. chromogenes, S. simulans, and S. xylosus isolated from their teat skin precalving were at increased odds of having an IMI with the same species postcalving. Overall, 44% of all heifers with a S. chromogenes IMI around the time of parturition had the same strain isolated from a body site. Based on pulsed-field gel electrophoresis, a high level of strain diversity was found.

Cross-sectional study to identify staphylococcal species isolated from teat and inguinal skin of different-aged dairy heifers.

The purpose of this study was to describe the prevalence and distribution of staphylococcal species on the teat and inguinal skin of dairy heifers across the various stages of the heifer life cycle. The cross-sectional study included 106 Holstein heifers with an age range of 0 d to 27 mo that were selected from 11 different groups, based on housing type and age, on a single dairy operation. A composite swabbing sample including all 4 teats and a second composite sample including both inguinal regions of each heifer were collected using gas-sterilized electrostatic dusters (Swiffers; Procter and Gamble, Cincinnati, OH). Swabbing samples were mixed with 10 mL of sterile saline, agitated, and cultured on mannitol salt agar plates. At 24 h, plates were read and up to 10 staphylococcal colonies were saved for further analysis. Staphylococcal isolates were speciated using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry or PCR amplification and partial sequencing of rpoB or tuf. The prevalence of staphylococci was compared between the inguinal and teat regions using the chi-squared or Fisher's exact test, as applicable. Logistic regression models were used to investigate the relationship between a heifer's age (treated as a quantitative continuous variable) and the probability of isolating a given staphylococcal species from a given body site (inguinal region or teats). Overall, the most common species identified were Staphylococcus haemolyticus followed by Staphylococcus chromogenes, Staphylococcus xylosus, Staphylococcus devriesei, and Staphylococcus sciuri. Staphylococcus aureus was more prevalent on the teat than in the inguinal region, whereas Staphylococcus arlettae was more prevalent in the inguinal region than on the teat. All other staphylococcal species were as likely to be found on the teat skin as the inguinal region skin. Isolation from the inguinal and teat skin was associated with age for Staphylococcus agnetis, S. chromogenes, S. devriesei, Staphylococcus equorum, S. haemolyticus, Staphylococcus lentus, S. sciuri, Staphylococcus vitulinus, and S. xylosus. The probability of finding S. chromogenes and S. agnetis on the teat and inguinal region increased with age, whereas the probability of S. devriesei and S. haemolyticus decreased with age. This study provides further insight into the ecology of staphylococcal species involved in heifer mastitis.

Subclinical hypocalcemia, plasma biochemical parameters, lipid metabolism, postpartum disease, and fertility in postparturient dairy cows.

A study was conducted to evaluate the potential association between Ca status at calving and postpartum energy balance, liver lipid infiltration, disease occurrence, milk yield and quality parameters, and fertility in Holstein cows. One hundred cows were assigned to 1 of 2 groups based on whole-blood ionized Ca concentration ([iCa]) on the day of calving [d 0; hypocalcemic [iCa] <1.0 mmol/L (n=51); normocalcemic [iCa] ≥ 1.0 mmol/L (n=49)]. Cows were blocked based on calving date and parity. Blood samples were collected approximately 14 d from expected calving date (d -14), the day of calving (d 0), and on d 3, 7, 14, 21, and 35 postpartum for measurement of plasma nonesterified fatty acid, iCa, total Ca, glucose, and total and direct bilirubin concentrations, and plasma aspartate aminotransferase and gamma glutamyl transferase activities. Liver biopsies were obtained from a subset of cows on d 0, 7, and 35 for quantification of lipid content. Milk samples were collected on d 3, 7, 14, 21, and 35 postpartum for measurement of somatic cell count and percentages of protein, fat, and solids-not-fat. Data for peak test-day milk yield, services per conception, and days open were obtained from Dairy Herd Improvement Association herd records. Disease occurrence was determined based on herd treatment records. Hypocalcemic cows had significantly higher nonesterified fatty acids on d 0. Hypocalcemic cows also had significantly more lipid in hepatocytes on d 7 and 35 postpartum. However, no statistically significant differences were observed between groups for plasma aspartate aminotransferase and gamma glutamyl transferase activities or total and direct bilirubin concentrations. Milk protein percentage was lower in hypocalcemic cows on d 21 and 35. However other milk quality variables (somatic cell count, milk fat percentage, and solids-not-fat) and milk yield variables (peak test-day milk yield and 305-d mature-equivalent 4% fat-corrected milk yield) did not differ between groups. No differences were observed between groups in the occurrence of clinical mastitis, ketosis, displaced abomasum, dystocia, retained placenta, metritis, or fertility measures (percentage cycling at 50-60 d postpartum, services per conception, or days open). These data suggest that early lactation fatty acid metabolism differs between cows with subclinical hypocalcemia and their normocalcemic counterparts.

Concentrations of nonesterified fatty acids and glucose in blood of periparturient dairy cows are indicative of pregnancy success at first insemination.

Greater blood concentrations of nonesterified fatty acids (NEFA) and lesser blood concentrations of glucose are indicative of the normal process of nutrient partitioning that occurs in early postpartum dairy cows. The objective was to determine the relationship between blood NEFA and glucose concentrations and subsequent conception at first insemination in postpartum dairy cows. Holstein (n=148) and Guernsey (n=8) dairy cows were blood sampled at approximately d 10, 7, and 3 prepartum, on the day of calving and 3, 7, 14, and 21 d postpartum for measurement of NEFA and glucose concentrations. Serum and plasma were harvested and used for measurement of NEFA and glucose concentrations, respectively. Cows were given a presynchronization treatment (2 injections of PGF(2α) 14 d apart) with the second PGF(2α) injection occurring 14 d before the initiation of the timed AI (TAI) protocol. Blood for determination of progesterone concentrations was collected at each presynchronization injection and at the initiation of the TAI protocol that was used for first insemination (74±7 d postpartum). Cows were considered noncycling if serum progesterone concentrations at the 2 presynchronization PGF(2α) injections (d 37 and 51±7 postpartum) and at the initiation of the TAI protocol (d 65±7 postpartum) were ≤1 ng/mL, and there was no indication of ovulation or presence of a corpus luteum by ultrasound examination at the initiation of the TAI protocol. Pregnancy was determined at 33 d and again at 61 d after first insemination by using ultrasound. Across all days, serum NEFA and plasma glucose concentrations were not different between cows that ovulated before the initiation of the TAI program (cycling) compared with those that did not ovulate (noncycling). Serum NEFA concentrations, however, were less and plasma glucose concentrations were greater during the early postpartum period for cows that subsequently became pregnant at first insemination compared with those that failed to become pregnant. Logistic regressions were used to predict the probability of pregnancy based on NEFA and glucose concentrations from individual days. The prediction with the greatest likelihood ratio was for d 3 postpartum NEFA and glucose concentrations. Nutritional status during the early postpartum period (within 1 wk after calving), as indicated by blood NEFA and glucose concentrations, may affect subsequent fertility by a mechanism that is independent from interval to first ovulation.

Invited review: ruminant ecology and evolution: perspectives useful to ruminant livestock research and production.

The article reviews ruminant ecology and evolution and shows insights they offer into livestock research. The first ruminants evolved about 50 million years ago and were small (<5 kg) forest-dwelling omnivores. Today there are almost 200 living ruminant species in 6 families. Wild ruminants number about 75 million, range from about 2 to more than 800 kg, and generally prefer at least some browse in their diets. Nine species have been domesticated within the last 10,000 yr. Their combined population currently numbers 3.6 billion. In contrast to wild ruminants, domestic species naturally prefer at least some grass in their diets, are of large body weight (BW; roughly from 35 to 800 kg), and, excepting reindeer, belong to one family (Bovidae). Wild ruminants thus have a comparatively rich ecological diversity and long evolutionary history. Studying them gives a broad perspective that can augment and challenge the status quo of ruminant research and production. Allometric equations, often used in ecology, relate BW to physiological measurements from several species (typically both wild and domestic). They are chiefly used to predict or explain values of physiological parameters from BW alone. Results of one such equation suggest that artificial selection has increased peak milk energy yield by 250% over its natural level. Voluntary feed intake is proportional to BW(0.9) across wild and domestic ruminant species. This proportionality suggests that physical and metabolic factors regulate intake simultaneously, not mutually exclusively as often presumed. Studying the omasum in wild species suggests it functions primarily in particle separation and retention and only secondarily in absorption and other roles. Studies on the African Serengeti show that multiple species, when grazed together, feed such that they use grasslands more completely. They support the use of mixed-species grazing systems in production agriculture. When under metabolic stress, wild species will not rebreed, but rather will extend lactation (to nourish their current offspring). This bolsters the suggestion that lactation length be extended in dairy operations. Cooperation between animal scientists and ecologists could generate more valuable insight.

Variability in in situ ruminal degradation parameters causes imprecision in estimated ruminal digestibility.

The ruminal digestibility of dietary ingredients is frequently estimated with degradation parameters (e.g., rate and extent of degradation). Mean degradation parameters (e.g., those in a feed library) are often used, but limited data suggest considerable variation around these means, potentially leading to imprecise digestibility estimates. This experiment quantified degradation parameter variation for forage hays and determined the impact of this variation on the precision of ruminal digestibility estimates. Degradation data were those previously published by our laboratory and included degradation rate, lambda(d) (h(-1)), fraction instantly degraded, a (g x g(-1)), potential extent of degradation, (a + b) (g x g(-1)), and fraction not instantly degraded that is potentially degradable, b (g x g(-1)) of alfalfa, grass, and grass-legume hays. Ruminal digestibilities of chemical fractions (dry matter, neutral detergent fiber, acid detergent fiber, hemicellulose, crude protein) were estimated using these data. Ninety-five percent confidence limits of digestibility were determined using propagation of uncertainty with measured standard deviations of degradation parameters. Values for coefficients of variation of degradation parameters were large; averaged across chemical fractions, they were 24.8, 28.6, 20.7, and 12.6% for lambda(d), a, b, and (a + b). Ninety-five percent confidence limits of digestibility were large (80.5% of digestibility means) and often overlapped each other, even when digestibility means differed greatly numerically. Consequently, digestibility values computed with mean degradation parameters may have little biological and practical significance. When uncertainty in all parameters but lambda(d) was set to zero (lambda(d) alone had uncertainty), 95% confidence limits still encompassed 54.5% of digestibility means. Thus, uncertainty in lambda(d) alone caused considerable imprecision in estimated digestibility. These results caution against using mean degradation parameters to estimate digestibility.

A mechanistic model for predicting intake of forage diets by ruminants.

Accurate voluntary feed intake (VFI) prediction is critical to the productivity and profitability of ruminant livestock production systems. Simple empirical models have been used to predict VFI for decades, but they are inflexible, restrictive, and poorly accommodate many feeding conditions, such as those of developing countries. We have developed a mechanistic model to predict VFI over a range of forage diets (low- and high-quality grasses and legumes) by wild and domestic ruminants of varying physiological states (growth, lactation, gestation, nonproductive). Based on chemical reactor theory, the model represents the reticulorumen, large intestine, and blood plasma as continuous stirred-tank reactors and the small intestine as a plug flow reactor. Predicted VFI is that which 1) fulfills an empirical relationship between chemostatic and distention feedback observed in the literature, and 2) leads to steady-state conditions. Agreement between observed and actual VFI was great (generally R(2) >0.9, root mean square prediction error <1.4 kg/d, CV <25%). Root mean square prediction error for our model was only 67% that of the Beef NRC (2000) model, the leading empirical prediction system for cattle. Together, these results demonstrate that our model can predict ruminant VFI more broadly and accurately than prior methods and, by consequence, serve as a crucial tool to ruminant livestock production systems.

Effects of calcium chloride and calcium sulfate in an oral bolus given as a supplement to postpartum dairy cows.

An oral calcium bolus (Bovikalc, Boehringer Ingelheim Vetmedica) supplying calcium to dairy cows in the form of calcium chloride and calcium sulfate was evaluated to determine the effect on calcium homeostasis immediately after calving. Cows in the treatment group received one bolus immediately after calving and a second bolus 12 hours later. Control cows received no calcium supplementation. Blood was analyzed for ionized calcium, and urine was collected for urinary pH determination. Postpartum supplementation with the Bovikalc bolus significantly increased serum ionized calcium levels and decreased urine pH values.

Efficacy of Solis, NovasilPlus, and MTB-100 to reduce aflatoxin M1 levels in milk of early to mid lactation dairy cows fed aflatoxin B1.

An experiment was conducted to determine the efficacy of 3 adsorbents, Solis (SO; Novus International Inc.), NovasilPlus (NOV; Engelhard Corp.), and MTB-100 (MTB; Alltech), in reducing aflatoxin (AF) M(1) concentrations in milk of dairy cows fed an AF-contaminated diet. Twelve early to mid lactation dairy cows averaging 163 d in milk were used in a 4 x 4 Latin square design with 3 replications. Cows were blocked by parity, body weight, and milk production and were provided ad libitum access to feed and water. Within each replicate, cows were randomly assigned to the 4 dietary treatments for 4 consecutive 7-d periods. Dietary treatments included AF [112 microg of AFB(1)/kg of diet dry matter (DM)]; AF + 0.56% SO; AF + 0.56% NOV; and AF + 0.56% MTB. Milk samples were collected on d 6 and 7 of each of the experimental periods. Feed intake, milk production, milk fat percentage, milk protein percentage, and linear somatic cell scores were not affected by dietary treatments and averaged 22.20 kg/d of DM, 33.87 kg/d, 3.78%, 2.95%, and 1.60, respectively, across all treatments. Transfer rates of AF from feed to milk averaged 2.65, 1.48, 1.42, and 2.52% for cows fed AF, AF + SO, AF + NOV, and AF + MTB, respectively. Daily AFM(1) excretion in milk averaged 66, 37, 35, and 63 microg/d for cows fed AF, AF + SO, AF + NOV, and AF + MTB, respectively. The addition of SO and NOV to the AF diet resulted in a significant reduction in milk AFM(1) concentrations (SO, 45%; NOV, 48%) and AFM(1) excretion (SO, 44%; NOV, 46%). In contrast, MTB was not effective in reducing milk AFM(1) concentrations (4%), AFM(1) excretion (5%), or AF transfer from feed to milk (2.52%). Results indicated that SO and NOV at 0.56% of the diet were effective in reducing milk AFM(1) concentrations in cows consuming a total mixed ration containing 112 microg of AFB(1)/kg of diet DM.

Comparing relative feed value with degradation parameters of grass and legume forages.

Relative feed value (RFV) was evaluated relative to in situ degradation parameters of grass and legume forages. Early-cut alfalfa (n = 20), late-cut alfalfa (n = 26), cool-season grass (n = 11), warm-season grass (n = 4), and grass-legume (n = 20) samples were collected from duplicate hay bales submitted to the 2002 and 2003 Missouri State Fair Hay Contests. Subsamples were incubated in the rumen of 2 lactating Holstein cows for 0, 6 or 8, 12, 24, and 48 h to determine in situ degradation of DM, ADF, NDF, CP, and hemicellulose over time. Degradation data were fit to a variety of candidate models to estimate degradation parameters. Correlation coefficients between degradation parameter estimates [sorted according to forage (early-cut alfalfa, late-cut alfalfa, grass, or grass-legume)] and RFV were determined. For further comparison, correlations between NDF degradation parameter estimates and digestible DMI were determined with data from a previous study. Degradation data were best fit to a single, gamma 2-distributed pool model without a lag phase. Relative feed value was significantly correlated (P < 0.05) with potentially digestible DM and CP for early-cut alfalfa, potentially digestible DM for late-cut alfalfa, and potentially digestible DM, NDF, and hemicellulose for grass-legume. The percentage of significant correlations (10.7%) across the entire data set was low and no correlations were significant for grass. Relative feed value did not account for the variation in degradation parameters, especially for grasses. A further correlation analysis, which compared digestible DMI with degradation parameter estimates reported from another data set, revealed that digestible DMI and degradation parameter estimates were related for grass but not for alfalfa forages. These results suggest that RFV is limited by its failure to include degradation parameters.

Relationship of thermal status to productivity in heat-stressed dairy cows given recombinant bovine somatotropin.

The responses of lactating Holstein cows to daily administration of bovine somatotropin (bST) were measured at thermoneutrality (Tn) and under both constant and cycled heat-stress conditions to determine the relationship between thermal status and bST-induced shifts in milk production. All tests included a 5-d acclimation period at Tn (18 degrees C), followed by a 2-d increase in ambient temperature to 28.5 degrees C. After d 3, ambient temperature was cycled between 28.5 (day) and 25.5 degrees C (night) for 4 d. Daily injections with either 31 mg of bST or saline began on d 1 of the experiment. Milk production, feed intake, and respiratory rate (RR) were measured daily. Intraperitoneal, telemetric temperature transmitters were used for a continuous measure of core body temperature (T(core)). Blood samples were collected during each phase to evaluate the changes in serum chemistry in response to bST and heat stress. Following a 15-d recovery, cows were switched across injection treatments and the study was repeated. Milk production decreased by approximately 18.4% below the initial yield at Tn by the end of 7 d of heat challenge. Although a reduction in milk production occurred during heat stress in both groups, milk production was higher in bST-treated cows compared with control cows during periods of constant and cyclic heat. Likewise, bST treatment during the entire period increased the milk-to-feed ratio over the control level by approximately 11.3%. Plasma insulin-like growth factor 1 and serum nonesterified fatty acids accompanied the increased growth hormone level with bST treatment (approximately 122.0 and 88.8%, respectively), whereas plasma urea nitrogen was reduced by approximately 13.3% to reflect the shift to lipid metabolism. There was no difference in T(core) of the treatment and control groups at Tn. Both bST and control cows increased RR and T(core) above the Tn level by approximately 94.8 and 2.9%, respectively, during constant heat, with a greater increase in T(core) of bST-treated compared with control cows (approximately 0.6%). The increase in RR during heat stress preceded T(core) by 1 d for both groups. During cyclic heat, T(core) decreased by approximately 0.4% compared with constant heat in both the control and bST-treated groups. Bovine somatotropin treatment increased milk production similarly during the Tn and heat-stress periods, approximately 8.3% over the control; however, the bST-induced increase in milk-to-feed ratio was greatest during the continuous and cyclic heat-stress phases, approximately 16.2%. This increase occurred together with the elevation in T(core).

Evaluation of ruminally protected methionine and lysine or blood meal and fish meal as protein sources for lactating Holsteins.

Forty lactating Holstein cows averaging 55 days in milk were used in a randomized block designed experiment to evaluate the effectiveness of ruminally protected Met and Lys compared with that of ruminally undegradable protein for supporting lactation. Cows were fed total mixed diets for 15 wk. Diets were formulated to be isonitrogenous with the same base ingredients resulting in base crude protein percentage of 15.5. Supplemental crude protein supplied by urea, soybean meal, or a 50:50 (wt/wt) mixture of fish and blood meal increased total dietary nitrogen to 18.0% of diet DM. Two additional diets consisted of the basal diets soybean meal and urea, which were supplemented with ruminally protected DL-Met and Lys-HCL at 10 and 25 g/d, respectively (soybean meal + amino acids (AA), urea + AA). Mean measures of dry matter intake, milk yield, milk protein percentage, and milk fat percentage were not affected by protein supplement. Milk protein yield, milk fat yield, casein yield, and casein percentage also were not affected by source of supplemental protein. Results indicate that at the level of crude protein intake relative to milk production in this experiment, the source of protein did not affect lactational performance.

Results of a nationwide survey to determine feedstuffs fed to lactating dairy cows.

A nationwide survey to determine feedstuffs used in the diets of dairy cows was conducted. This survey was mailed to dairy nutritionists at universities in each state to describe the use of 144 feedstuffs. Twenty-eight states responded and were grouped by region as follows: Northeast (Maine, Maryland, New Hampshire, New York, Ohio, Vermont, and West Virginia), Northwest (Idaho, Oregon, and Washington), Midwest (Iowa, Illinois, Michigan, Minnesota, Missouri, Nebraska, North Dakota, South Dakota, and Wisconsin), Southeast (Florida, Georgia, Kentucky, South Carolina, Tennessee, and Virginia), and Southwest (Arizona, Oklahoma, and Texas). Comparisons of the feedstuffs most commonly fed, the maximum inclusion rate of feedstuffs in the diet, and how these feedstuffs were fed (alone or in a mixed diet) were made. The maximum percentage fed was also reported. Overall, concentrate feeds were fed blended with other ingredients more often (98.7% of the time) than forages (67.8% of the time). Also, forage was fed at a higher percentage (42.3%) of the total diet relative to individual concentrate ingredients (16.3%). Corn silage, soybean meal, corn grain, alfalfa hay, and grass hay were common feeds across all regions. However, the use of by-product feeds was variable depending on local availability.

Effect of fibrous by-products on production and ruminal fermentation in lactating dairy cows.

Lactating dairy cows were used in experiments to determine the effects of feeding a combination of fibrous by-products to replace a portion of alfalfa hay or grain. Cows were fed a control diet, consisting of alfalfa hay, corn, soybean meal, and corn silage or one of four treatment diets. In these diets, a combination of soy hulls, corn gluten feed, and wheat midds replaced approximately 30 or 60% of alfalfa hay or 25 or 50% of corn and soybean meal. A 56-d production study used 50 midlactation dairy cows in a randomized complete block design. No differences in milk production or composition among treatments were measured, except for the diet in which 60% of the alfalfa hay was replaced with fibrous by-products. Cows fed this diet had a significantly lower percentage of milk fat compared with other treatments. A fermentation study used five fistulated, multiparous lactating dairy cows in a 5 x 5 Latin square design. Cows were fed one of the five experimental diets used in the production study during five consecutive 14-d periods. Rumen acetate to propionate ratio was highest for the control and 50% concentrate replacement diets (3.27) and lowest for the 60% hay replacement diet (2.78). This shift in ruminal volatile fatty acid profile corresponded to the change in milk fat percentage, measured during the production study. A mixture of fibrous by-products fed as an alternative to hay or grain ingredients could potentially decrease feed costs without a resultant decrease in milk production by mid-lactation dairy cows.

Effects of controlled heat stress on ovarian function of dairy cattle. 1. Lactating cows.

The objective of this experiment was to determine the effects of controlled heat stress on ovarian function of lactating dairy cows. Estrus was synchronized (estrus = d 0), and cows were randomly assigned to either heat stress (n = 11; 29 degrees C, 60% relative humidity) or thermoneutral (n = 11; 19 degrees C, 60% relative humidity) treatment. For cows undergoing heat stress, ambient temperature (19 degrees C) was increased from d 11 to 13 of the estrous cycle (3.3 degrees C/d increase) and remained at 29 degrees C until d 21. Beginning on d 11, the growth and regression of ovarian follicles and corpora lutea were measured by using ultrasonography. Blood was collected daily by coccygeal venipuncture for measurement of serum concentrations of progesterone and estradiol. The second wave dominant follicle was more likely to ovulate in cows in the thermoneutral treatment than in cows undergoing heat stress (91 vs. 18% ovulation, respectively). Patterns of follicular growth in cows under-going heat stress were associated with decreased serum estradiol from d 11 to 21 and on the day of luteolysis. The average day of luteolysis was delayed by 9 d in heat-stressed cows. Conclusions were that follicular growth and development and luteolytic mechanisms were compromised in heat-stressed cows; as a result, luteolysis was delayed, and second wave dominant follicles did not ovulate.

Supplementation of nicotinic acid for lactating Holstein cows under heat stress conditions.

Twenty-six lactating Holstein cows (90 d of lactation) were blocked according to milk production, parity, and days of lactation for assignment to one of two dietary treatments. Diets included a control diet with no supplemental niacin and a diet supplemented with increasing concentrations of niacin (12, 24, or 36 g/d per cow over three consecutive 17-d periods. Cows were housed in a covered free-stall barn and were fed and milked twice daily. Mean maximum air temperatures and temperature-humidity indexes were 28.5, 31.4, and 25.2 degrees C and 79.6, 85.1, and 75, respectively, for the three periods. Rectal temperature was measured with a rectal probe, tail and rump temperatures by infrared thermometry, and respiratory rate by visual observation. Measurements were made daily at 0800, 1600, and 2200 h. Rectal temperature was not affected by treatment. Comparison of skin temperatures for control cows and cows fed niacin showed higher temperatures at the tail (34.0 vs. 33.7 degrees C at 0800 h; 35.1 vs. 34.8 degrees C at 1600 h, respectively) and rump (34.1 vs. 33.7 degrees C at 0800 h; 35.3 vs. 35.0 degrees C at 1600 h, respectively) for control cows during period 1. No differences in thermal responses were observed during period 3. Niacin did not significantly increase milk production but decreased skin temperatures during periods of mild or severe heat stress.

Effects of supplemental shade on thermoregulatory response of calves to heat challenge in a hutch environment.

Holstein (n = 12) and Guernsey (n = 6) calves, housed in hutches, were used to evaluate the complex relationships among external environment, housing microclimate, and thermal status of calves. The study was conducted during the summer; 9 calves were housed in hutches under supplemental shade, and 9 calves were maintained in hutches under direct sunlight. Environmental and calf temperatures were measured twice daily at 0700 and 1500 h, which included determinations of air temperature, inner and outer surface temperatures of the hutch, rectal and skin temperatures of the calf, and respiration rate. Outer and inner surface temperatures of the hutch were lower under supplemental shade. Hutch air temperature was highly correlated with inner surface temperature and therefore was lower in the shaded environment. During the p.m. period, when heat stress was highest, calves housed in a shaded hutch environment had lower skin temperatures and respiration rates than did unshaded calves. Body temperature and respiration rates increased less for calves in shade than for calves in sun. These data define the relationship between the calf and the environment. Supplemental shade diminished the severity of heat stress experienced by calves that were housed in hutches during the summer.

Influence of by-product feeds and tallow on lactation performance of Holstein cows during two seasons.

Experiments were conducted to evaluate the impact of fibrous by-product feeds and tallow on lactation performance and ruminal fermentation. Diets were arranged as a 2 x 2 factorial of low and high NDF with or without added tallow. Corn and soybean meal were replaced with corn gluten feed, soyhulls, wheat middlings, and high moisture, whole ear corn. Forty-eight Holstein cows were used in two seasonal replicates of a randomized block design. Addition of tallow decreased intake of the low fiber diet, but not the high fiber diet, during winter. Intake was unaffected by diet during summer. Dietary NDF percentage did not change DMI. Milk production was unaffected by addition of tallow but was more persistent for cows fed low fiber diets. Tallow reduced milk protein percentage but did not change milk fat percentage. Fibrous feeds did not influence milk composition. Four fistulated cows were used in a 4 x 4 Latin square design. Fibrous by-product feeds decreased total VFA concentration. Acetate to propionate ratio increased when tallow was added to high fiber diets but decreased when tallow was added to low fiber diets. Tallow and fibrous by-product feeds can be used to support milk production.

Evaluating effects of fish meal on milk fat yield of dairy cows.

Experiment 1 measured the effect of different amounts of dietary fish meal on milk yield and composition. Milk fat percentage and yield were decreased by increased fish meal intake, but this change was not associated with changes in ruminal fermentation patterns. Plasma long-chain n-3 polyunsaturated fatty acids were increased as intake of fish meal increased. Ruminal disappearance of DM, CP, and lipid in fish meal was measured in situ. Seventy percent of lipid disappeared by 8 h. Intraruminal administration of fish oil did not alter ruminal fermentation and only slightly changed fatty acid profiles in duodenal digesta, plasma, or milk. Duodenal infusion increased plasma n-3 fatty acids but did not affect composition of fatty acids in milk. Experiment 2 compared effects of dietary fish meal and fish oil on milk production and composition. Fish meal increased n-3 fatty acids in plasma compared with those of the fish oil treatment. No changes were found in milk yield or composition because of experimental treatments. Cows fed fish meal or fish oil differed significantly in plasma fatty acid profiles but did not differ in ruminal VFA concentrations or milk fat yield.