Technical note: covariance adjustment in beef cattle research.

In randomized experiments, analysis of covariance is used to increase precision of treatment comparisons. However, for factors that are observational (e.g., breed) or for covariates measured after treatments are applied, it may not be biologically meaningful to calculate treatment means adjusted to a common value of the covariate. For example, in beef cattle trials, it may not be meaningful to compare hot carcass weights of medium- and large-framed breeds adjusted to a common weaning weight because the breeds have naturally different mean weights at weaning. If done, this would typically result in an undesirable downward adjustment of mean carcass weight for the large-framed breed and upward adjustment of the mean carcass weight for the small-framed breed. However, it is desirable to evaluate the mean carcass weight for two diets, adjusted to a common weaning weight. Because of randomization, the expected weaning weights of animals on the two diets are equal and hence the only effect of covariance adjustment is to increase precision of the diet comparison. This paper presents the statistical methodology for estimating covariance adjusted means (termed partially adjusted means) when the levels of some of the factors are compared at a common value of the covariate but the levels of other factors are compared at differing values of the covariate. The methodology is extended to include several covariates, several factors, and arbitrary interactions among covariates, among factors, and between factors and covariates. These methods can be implemented using existing statistical software for linear models. Data are presented from an experiment in which hot carcass weight was recorded for beef cattle. Analyses of these data illustrate that adjusted means, partially adjusted means, and unadjusted means may differ substantially in magnitude, significance, and in the ranking of treatments.

A three-day weighed food record and a semiquantitative food-frequency questionnaire are valid measures for assessing the folate and vitamin B-12 intakes of women aged 16 to 19 years.

The purpose of this study was to validate a food-frequency questionnaire (FFQ) and a 3-d weighed food record (3d-WFR) by comparing nutrient intakes estimated using these methods with serum folate, RBC folate and serum vitamin B-12 concentrations in 105 females aged 16-19 y. During an early morning clinic visit, subjects completed a self-administered, 116-item FFQ, blood was collected and they were trained to complete a 3d-WFR. Folate intakes as determined by the 3d-WFR (r = 0.65, P < 0.01) exhibited a stronger association with serum folate than did intakes from the FFQ (r = 0.48, P < 0.01) (P = 0.017). The correlations between folate intakes and RBC folate as determined by the FFQ (r = 0.42, P < 0.01) and 3d-WFR (r = 0.50, P < 0.01) methods did not differ. Vitamin B-12 intakes showed only a modest association with serum vitamin B-12 when supplement users were included in the analyses (FFQ, r = 0.25, P < 0.05; 3d-WFR, r = 0.32, P < 0.05). After excluding supplement users from the analyses, the relationship between vitamin B-12 intakes as determined by FFQ and serum vitamin B-12 was no longer significant. Median daily folate intakes (346 vs. 212 microgram) and vitamin B-12 (4.9 vs. 1.9 microgram) estimated from the FFQ were higher than those obtained from the 3d-WFR. In sum, these data suggest that both the FFQ and 3d-WFR are valid measures of assessing the folate intake of young women, and both appear to be useful in determining vitamin B-12 intake when supplemental users are included. The markedly different conclusions about absolute folate and vitamin B-12 intakes obtained using these two dietary methodologies should be taken into consideration when making recommendations about optimal folate intakes in relation to disease prevention.

The effect of the Hurnik-Morris (HM) system on sow locomotion, skin integrity, and litter health.

Gilts (n = 187) were randomly assigned to either the Hurnik-Morris housing system (HM) or a conventional gestation crate system (GC) prior to breeding. The Hurnik-Morris system provides housing for sows in small groups. Gilts were synchronized for estrus and bred to Duroc Hampshire commercial crossbred boars. Gilts were reared in their respective housing systems through their gestation period. Housing system during breeding and gestation of sows did not affect their respective piglet mortality and piglet viability levels. The slightly higher feet and leg problem scores for the HM sows at weaning may indicate a necessity for farrowing accommodation that will allow movement of sows during lactation.

Folate bioavailability from milk-containing diets is affected by altered intestinal biosynthesis of folate in rats.

This study was designed to assess the effect of succinylsulfathiazole on the apparent bioavailability of folate added to milk-containing diets. We also evaluated the impact of milk type on the relative bioavailability (bioavailability) of folate following pasteurization (62.5 degrees C, 30 min) and on the bioavailability of folic acid (PteGlu) vs. pteroylhexa-gamma-L-glutamic acid (PteGlu6). Following folate depletion (5 wk), 108 rats (six per group) were fed for 4 wk diets with or without 20 g milk solids/100 g diet and containing PteGlu, PteGlu + 5 g/kg succinylsulfathiazole, or PteGlu6. Folate bioavailability was determined using plasma folate concentration and a standard curve generated from rats fed milk-free diets with graded levels of PteGlu. The PteGlu and PteGlu6 bioavailability from human milk-containing diets was twice that of diets containing cow or goat milk (P < 0.05). Incorporation of a sulfa drug into diets containing human or cow milk reduced PteGlu bioavailability by one half (P < 0.05). Further, the values for bioavailability of PteGlu from diets containing human or goat milk no longer differed (0.86 and 0.75, respectively), and bioavailabilities from human milk- and goat milk-containing diets were greater than that of the cow-milk-containing diet (0.54) (P < 0.05). Pasteurization of milk did not influence folate bioavailability. The bioavailability of PteGlu6 was 49-71% that of PteGlu (P < 0.05). In summary, milk type differentially affects intestinal folate biosynthesis, and the superior folate bioavailability from human milk-containing diets is due in part to enhanced intestinal biosynthesis of folate.

Effects of forage particle size and long hay for cows fed total mixed rations based on alfalfa and corn.

A 2 x 2 factorial arrangement of treatments, in which particle length of alfalfa silage in the TMR and supplementary long alfalfa-grass hay were the factors, was used to determine whether hay benefits lactating cows and whether its effects depend on fibrosity of the main forage source. Without supplementary hay, TMR contained 45% forage, including corn silage, and 26 to 27.5% NDF. When hay was fed, the amount of alfalfa silage in the corresponding TMR was reduced. In the production trial, 40 cows (20 multiparous) were fed the diets for 8 wk in early lactation. No interactions of silage length and hay occurred on any production variables except lactose concentration in the milk of multiparous cows. Addition of hay to the diet enhanced DMI, without effect on production, so efficiency of milk production was reduced. Shorter alfalfa silage enhanced DMI by multiparous cows, reduced SCM and FCM in primiparous cows, and depressed fat test in both groups. Milk composition and component production generally were unaffected. Five rumen-fistulated cows in early to midlactation each were given the four treatments during four 3-wk periods. Hay enhanced rumination when short alfalfa silage was fed but tended to reduce it on long alfalfa silage. Hay also depressed rumen pH and enhanced VFA concentrations. Alfalfa silage length had minimal effects on rumination and no effect on fermentation, and neither hay nor silage length affected digestion of silage DM or NDF in the rumen. Addition of hay to the diet may not be beneficial for cows fed TMR, but longer term feeding studies are needed.

The behavior of gestating swine housed in the Hurnik-Morris system.

A group housing system for sows, the Hurnik-Morris (HM) system, was developed to address several of the perceived animal welfare limitations of existing housing methods. The HM system permits socially coordinated eating and resting, controlled and socially undisturbed feed intake, physical exercise, and regular exposure to boars. The HM system effectively uses and reinforces the behavioral phenomenon of the social synchronization of feeding and provides a less restrictive housing environment. The system provides housing for sows in small groups and an individual, non-competitive feeding environment using electronic feeding compartments. Gilts reared during gestation in the HM system were observed to spend less time lying in sternal recumbency (31 vs 21%; P = .004) and performing stereotypies (.10 vs .56%; P = .034) and to spend more time participating in social activities (1.4 vs .19%; P = .0007) than similar gilts kept in gestation crates (GC). The HM sows revealed a significantly longer latent period to postprandial lying than did GC gilts (64 vs 32 min; P = .0001). The order of gilt entry into the feeding compartments tended to be more consistent than the sequence of feeding compartments being entered (W = .57 vs .41; P = .06). This indicates that social factors seemed to be more important than spatial ones in determining the order of entry into the feeder compartments.

Patterns of stillbirth and dystocia in Ontario cow-calf herds.

The association between a number of individual animal and herd level factors and calving problems in beef cows and heifers were examined. Data were from the 1987 calving season for a subset of 123 herds which maintained individual-animal records, from a sample of 180 randomly selected Ontario cow-calf herds. The median herd dystocia rate was 5.8% and 24.4% of herds had no dystocias. The median herd stillbirth rate was 2.8%, and 33.3% of herds had no stillbirths. Dystocias and stillbirths were much more common in heifers than in cows. Separate statistical models of dystocia and stillbirth for cows and heifers were created. Dystocia in cows was associated with calf sex, previous calving assistance and large breed type and birth weight. Variations in 1987 cow herd dystocia rates were associated with calving season, location and density, and the herd dystocia rate in 1986. Dystocia in heifers was associated with large breed type and calf birth weight. Herd-level management practices associated with increased heifer dystocia rates included breeding heifers to calve earlier than cows and rearing heifers together with the cow herd. Stillbirths for both cows and heifers were associated with calving assistance, particularly hard assistance. Herd-level management and other factors were unassociated with stillbirths.

Culling practices of Ontario cow-calf producers.

This study describes the distribution of herd culling rates for 123 Ontario cow-calf herds maintaining individual animal records. Associations between culling and factors at both the individual and herd level were examined. In addition, the relative importance of individual animal and herd level influences on culling were investigated. The following individual cow culling risk factors: nonpregnancy, age, weaning weight index, calf outcome, abortion, prolapsed vagina, prolapsed uterus, calving injury, lameness and mastitis or udder problems were significantly associated with culling (p less than 0.01). Two herd level factors were associated with increased culling rates: a higher than average proportion of heifers and a shorter than average calving season (p less than 0.01). The proportion of culling variation attributed to individual animal and herd level influences varied with model type. While simple models (one-way ANOVA) indicated that the herd variance component for culling was relatively minor, more complex models indicated larger herd-to-herd variability (mixed model ANOVA). Thus, it appeared that the probability of culling for a cow with a given set of risk factors depended to an important extent on manager decisions in the herd of origin.

The effect of feeding frequency and meal size on amounts of total and parotid saliva secreted by sheep.

Total and unilateral parotid saliva production during eating were measured in response to offering sheep a fixed amount of lucerne (Medicago sativa) hay as one, two, four or eight meals. Total saliva measurements were obtained using sham-fed oesophageal-fistulated sheep. Unilateral parotid saliva was collected from sheep fitted with reversible re-entrant cannulas. Dry matter intakes and eating times were measured for each meal but were not constrained to particular values. Total and unilateral parotid saliva production during eating increased linearly with the log of the number of meals (P = 0.0001). The amounts corresponding to one, two, four and eight meals of lucerne hay were 1553, 1737, 1851 and 2087 ml during total collections and 209, 248, 307 and 352 ml during unilateral parotid collections. The time-period spent eating and the amount of food consumed both increased as meal number increased. Total saliva collections when lucerne hay was sham-fed as one, two, four or eight meals were associated with eating times of 56.9, 57.4, 70.8 and 86.0 min and intakes of 562, 622, 629 and 638 g dry matter respectively. For unilateral parotid collections, eating times and dry matter intakes were 64.2, 71.3, 78.0, 82.1 min and 515, 579, 614 and 627 g for one, two, four and eight meals of lucerne hay respectively. The saliva production response appeared to be determined through the effects of the time-period spent eating and amounts consumed, but other undetermined effects of feeding frequency contributed to the response. The importance of meal duration on total saliva production was assessed by sham-feeding of 800 g lucerne as stem, leaf, hay, chopped hay or ground and pelleted hay. Increasing meal duration by feeding with stems resulted in the production of 1808 ml saliva, whereas the rapid consumption of pellets resulted in only 442 ml being produced.

The effect of fasting time on plasma total cholesterol concentration in Mongolian gerbils.

This study investigated the effect of length of fasting time on plasma total cholesterol response of male Mongolian gerbils (Meriones unguiculatus). Plasma cholesterol levels from fed and fasted gerbils were also compared with those reported for humans under similar metabolic states. Plasma total cholesterol response showed a significant quadratic relationship with time over a 15-hour period. Between 6 and 9 hours of fasting (the time during which plasma triglyceride concentration became relatively constant), the average plasma total cholesterol concentration was 178 mg/dl, compared with a zero hour (fed) cholesterol level of 265 mg/dl. The difference in plasma cholesterol levels observed in fed and fasted gerbils is unlike what has been reported for humans. Results from most human studies show no differences in plasma total cholesterol concentrations for fed and fasted subjects. Failure to consider species differences in metabolic responses may have implications when results from animal experiments are extrapolated to humans.

Long-term feeding of casein or soy protein with or without cholesterol in Mongolian gerbils. II. Plasma lipid and liver cholesterol responses.

Male Mongolian gerbils (Meriones unguiculatus) were fed casein or soy protein in the presence and absence of dietary cholesterol for 15 months. Diets resembled the average North American diet in energy contributions from protein, fat and carbohydrate, cholesterol content and fatty acid profile. At month 0, 3, 6, 9, 12 and 15, plasma samples were analyzed for total cholesterol (TC), HDL cholesterol (HDLC) and triglyceride (TG) concentrations. Plasma LDL cholesterol (LDLC) was estimated indirectly. Liver TC was also determined at these time points. Comparisons of protein source and cholesterol level were averaged over the 15 month period. Casein-fed gerbils had significantly higher plasma TC and TG levels and lower HDLC levels (as a percent of TC) compared to soy-fed animals, independent of the presence or absence of dietary cholesterol. LDLC was significantly elevated in casein-fed gerbils only when cholesterol was present in the diet. Elevations in plasma TC levels were reflected by elevations in liver TC. Despite plasma lipid elevations that are consistent with the development of atherosclerosis (AS) and coronary heart disease (CHD) in humans, hyperlipidemic gerbils do not develop AS. Further characterization of gerbil lipid metabolism responses to dietary alterations aimed at the prevention of CHD in humans is necessary to elucidate the mechanism for the gerbil's resistance to AS.

Cytotoxicity of Mycoplasma mycoides subspecies mycoides for cultured endothelial cells.

Toxic effect of 5 SC- and 4 LC-type strains of Mycoplasma mycoides subspecies mycoides has been demonstrated in cultured endothelial cells. The SC strains are agents of contagious bovine pleuropneumonia and presumably specific for cattle although occasionally isolated from goats. The LC strains produce an acute septicemic disease in goats and a few strains have been reported in cattle. The tissue culture cytotoxic dose causing 75% cell death (TCCD75) was calculated for each strain. Cytotoxicity ranged from 0.9 X 10(9) to 12.0 X 10(9) when strains were tested in bovine endothelial cells with the SC strains being twice as cytotoxic as the LC strains on average. Strains G175/78 and D44 representing the most cytotoxic SC and LC strains respectively, were selected for comparative experiments using bovine, caprine and porcine endothelial cells, bovine embryonic lung fibroblast cells (BELF) and the bovine cell line Madin-Darby kidney cells (MDBK). Strain G175/78 was significantly more cytotoxic for bovine endothelial cells than caprine and porcine, suggesting that the cytotoxicity reflects specificity for the bovine species. This strain was also cytotoxic for BELF but not for MDBK cells indicating that not all bovine cells are susceptible. Conversely, cytotoxicity of strain D44 was not significantly different in any of the endothelial cells tested, although cytotoxicity for BELF was significantly different, the cytotoxicity of the LC strains seems to be of less specificity.

Estimation of phenotypic selection differentials for predicting genetic responses to ratio-based selection.

Ratios of the phenotypic values of two traits may be used as selection criteria in animal and plant breeding to improve the ratio traits themselves or to effect changes in their two component (numerator and denominator) traits. Prediction of genetic responses to ratio-based selection would facilitate quantitative analysis and evaluation of selection based on ratios. Methods for predicting such responses are derived and presented here. They employ expressions for the truncation value of a ratio and for the phenotypic selection differentials of the numerator and denominator traits. The derivation of these expressions is based upon the assumption that the phenotypic values of each of these traits are normally distributed. Worked examples relating to livestock and crop improvement are included to demonstrate how responses to selection for ratios may be predicted.

The effect of ambient temperature and type of wound on healing of cutaneous wounds in the common garter snake (Thamnophis sirtalis).

The effects of ambient temperature (13.5 degrees C, 21 degrees C, 30 degrees C) and type of wound on healing of skin wounds were evaluated in common garter snakes (Thamnophis sirtalis). Linear unsutured incisions and circular excisional wounds were evaluated grossly and microscopically in three snakes held at each temperature at each of two, five and ten days after surgery. Linear sutured and unsutured incisions and circular and square excisional wounds were similarly evaluated three and six weeks after wound production in groups of six snakes held at each temperature. The rates of stabilization of wound margins, scab formation, migration and maturation of the regenerating epithelium, resolution of dermal inflammation, and fibroplasia varied directly with temperature. The inflammatory reaction to wounding was similar in character and intensity in snakes held at all three temperatures two days after surgery. Unsutured linear incisions, compared to sutured incisions, tended to have more rapid epithelial maturation and a less intense inflammatory response. Healing of square and circular excisional wounds was similar; contraction of round wounds was slightly more irregular and, at a few observations, dermal maturation was slower and inflammation more widespread. It was concluded that healing of skin wounds can be accelerated by holding reptiles at the upper end of their voluntary temperature range. Wounds, if possible, should be created along the axis of lines of skin tension. Suturing small incisional wounds may not be advantageous.

The effect of certain topical medications on healing of cutaneous wounds in the common garter snake (Thamnophis sirtalis).

The effects of four topical medications on the rate and character of healing of cutaneous wounds were studied in six common garter snakes (Thamnophis sirtalis) held at an ambient temperature of 30 degrees C. Two sets of five 6 to 8 mm round excisional wounds, four test and one control site in each set, were created on the dorsolateral body wall of each snake. Wounds were examined daily and treated for ten days, then the snakes were killed and sections of all wounds were examined by light microscopy. Composite scores, derived by ranking each treatment group in relation to the control group (control score = 0) for each of 22 characteristics associated with wound healing, were used to compare the overall effects of each treatment. Statistical comparisons were made between groups for 20 characteristics. Wounds treated with a polyurethane film merited a score of +12 and had significantly more advanced healing than untreated controls for three characteristics. Wounds treated with an ointment containing scarlet red scored +6 but healing was not significantly greater than controls. Wounds treated with an antibacterial spray powder and an antibacterial ointment healed more slowly than controls and had scores of -6 and -12 respectively.

A source of cutaneous maternal semiochemicals in the mink?

Unique hypertrophic apocrine sweat glands are described in the neck, perineal and inguinal skin of mink kits. These glands enlarge after birth, only to regress rapidly and become vestigal by weaning. No similar phenomenon has been recognized before in mammals. Behavioral studies indicate a possible role for the glandular secretion in maternal recognition of the young.

Effect of dietary zinc deficiency on the endogenous phosphorylation and dephosphorylation of rat erythrocyte membrane.

The effect of dietary zinc deficiency on patterns of phosphorylation and dephosphorylation of rat erythrocyte membrane proteins and erythrocyte filterability was examined. Weanling male Wistar rats were fed an egg white-based diet containing less than 1.1 mg zinc/kg diet ad libitum for 3 wk. Control rats were either pair-fed or ad libitum-fed the basal diet supplemented with 100 mg zinc/kg diet. Net phosphorylation and dephosphorylation of erythrocyte membrane proteins were carried out by an in vitro assay utilizing [gamma-32P]ATP. The membrane proteins were subsequently separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and the 32P content of gel slices was counted by Cerenkov counting. Erythrocyte filterability was measured as the filtration time of suspensions of erythrocytes, both untreated and preincubated with diamide, under constant pressure. Erythrocyte ghosts from zinc-deficient rats demonstrated greater dephosphorylation of protein bands R1 plus R2 and R7 than pair-fed rats and greater net phosphorylation of band R2.2 than pair-fed or ad libitum-fed control rats (P less than 0.05). Erythrocytes from ad libitum-fed control rats showed significantly longer filtration times than those from zinc-deficient or pair-fed control rats. In conclusion, dietary zinc deficiency alters in vitro patterns of erythrocyte membrane protein phosphorylation and dephosphorylation, whereas the depression in food intake associated with the zinc deficiency increases erythrocyte filterability.

Effect of prepartum energy, body condition, and sodium bicarbonate on health and blood metabolites of holstein cows in early lactation.

Effects of prepartum energy and of postpartum sodium bicarbonate (0, .75% DM) on health were studied in two trials. In trial 1, 36 cows consumed either 102, 131, or 162% of their energy requirement in the dry period. Postpartum glucose and D(-)-3-hydroxybutyrate levels indicated that 131% group (between wk 1 and 2) and 162% group (over the first 4 wk) were closer to a ketotic state than treatment groups at other times. Displaced abomasums occurred more frequently in the 162% group than either the 102 or 131 group. Sodium bicarbonate did not alter the health. In trial 2, 40 cows were used to evaluate the effects of prepartum energy for a longer period. Energy treatments imposed in late lactation and in the dry period were 1) cows fed to requirement in both periods; 2) cows overfed in the first and underfed in the second period; 3) cows fed to requirement in the first and overfed in the second; 4) cows overfed in both periods. Blood metabolites and health measures were not affected by energy or sodium bicarbonate treatments. Overconsumption of energy by prepartum cows should be avoided; however, for a short period, overconsumption did not produce major health problems.

Effect of prepartum energy, body condition, and sodium bicarbonate on production of cows in early lactation.

In trial 1, the effects of dietary energy (102, 131 or 162% of requirement) in the dry period and of sodium bicarbonate (0 or .75% of diet dry matter) in early lactation were assessed with 31 cows in a 3 X 2 factorial arrangement of treatments. Body condition and weight increased linearly with prepartum energy. Dry matter intake and milk yield were similar across treatments through 12 wk postpartum. Sodium bicarbonate increased milk fat content only in the 131% group, an effect apparently related to greater mobilization of fat in that group. In trial 2, energy treatments imposed in late lactation (145 to 55 d prepartum) and in the dry period (55 to 0 d) were 1) cows fed to requirement in both periods, 2) cows overfed in the first and underfed in the second period, 3) cows fed to requirement in the first and overfed in the second period, and 4) cows overfed in both periods. Cows in treatments 1 and 2 (normal) calved in a thinner state than those in 3 or 4 (fat). In the first 12 wk postpartum, intake did not differ, but cows in groups 3 and 4 produced more milk. Sodium bicarbonate imposed factorially postpartum increased milk fat content. Overconsumption of energy prepartum did not impair production when high energy total mixed rations were fed postpartum.

Decline in serum zinc level throughout adult life in the laboratory mouse.

The objective of the study was to test the hypothesis that age and serum zinc level exhibit a negative correlation in the adult mouse. Fifty-seven male CBA/J mice were fed ad libitum, for 14 days, a semisynthetic diet containing 8 micrograms zinc per gram, a level that meets but does not exceed the weanling growth requirement for this nutrient under our conditions. At the end of the feeding trial the mice ranged in age from 7 to 87 weeks. Regression analysis indicated a linear decrease in serum zinc level with advancing age throughout adult life (Y = 0.70 - 0.0029 X, where Y is zinc level in micrograms/ml and X is age in weeks). The relationship was not changed significantly when adjusted for the effects of serum protein concentration, initial live weight, or 14-day weight gain and feed intake. The results suggest that the dietary zinc requirement increases progressively as an age-related phenomenon.