Influence of Grazing on Canola Grain, Canola Forage Yield, and Beef Cattle Performance.

Interest is increasing in grazing winter canola (Brassica napus) as an alternative crop in winter wheat (Triticum aestivum) rotations in the Southern High Plains (SHP) of the USA and similar environments. In this stidy, winter cereal rye (Secale cereale) and winter canola pastures (forage) were compared for two winter growing seasons at New Mexico State University's Rex E. Kirksey Agricultural Science Center at Tucumcari, NM, USA, to determine the relative effect of pasture type on late-gestation beef cows and growing yearling cattle, along with the effect of grazing on canola grain production. Canola grain yields were reduced by 25% when canola was grazed until removal approximately one month after grazing was initiated, but before the onset of rapid regrowth after winter (641 vs. 486 kg grain ha-1 for never grazed or grazed canola, respectively, p < 0.0256). No differences existed for forage mass, nutritive value, or animal performance, although forage mineral composition of canola could be a concern. Grazing winter canola as a dual-purpose crop in the SHP and similar environments is feasible when proper grazing management is applied; producers should anticipate a 20-25% reduction in grain yield, but expect animal gains to offset that loss.

Effects of administration of a growth promoting implant during the suckling phase or at weaning on growth, reproduction, and ovarian development in replacement heifers grazing native range.

Management strategies utilized during pre-breeding development of replacement heifers can impact fertility and the ovarian reserve. Angus-Hereford crossbred heifers (n = 233) were utilized over a 3-yr period to determine the effects of administration of a growth promoting implant at either branding or weaning on growth, reproduction, and ovarian development. Heifer calves were randomly assigned to one of three treatments: 1) nonimplanted controls (CON; n = 79), 2) implanted at approximately 2 mo of age (average calf age = 58 d) with Synovex-C (BIMP, n = 82), or 3) implanted at approximately 7 mo of age (average calf age = 210 d) with Synovex-C (WIMP; n = 72). In years 2 and 3, a subset of heifers (year 2 n = 16; year 3 n = 14) were unilaterally ovariectomized. Heifers implanted at 2 mo of age were heavier at weaning, yearling (mid-February; average calf age = 332 d), and at the beginning of the breeding season (P < 0.01) compared to CON and WIMP heifers. Average daily gain (ADG) was similar among treatments from weaning to yearling and weaning to the start of the breeding season (P ≥ 0.61); however, WIMP heifers had increased (P = 0.05) ADG from yearling to the start of the breeding season compared to BIMP heifers. Antral follicle count and reproductive tract scores were not influenced by implant treatment (P ≥ 0.18). Response to synchronization of estrus was increased (P = 0.02) in WIMP compared to CON heifers, with BIMP heifers similar to all other treatments. First service conception rates tended to be increased (P = 0.09) in CON heifers compared to WIMP heifers, with BIMP heifers similar to CON and WIMP. Final pregnancy rates were similar (P = 0.54) among treatments. A treatment × yr interaction was detected (P = 0.01) for the number of primordial follicles/section with increased primordial follicles in WIMP heifers in year 3 compared to BIMP and WIMP heifers in year 2 and CON heifers in year 3, as well as in BIMP compared to WIMP heifers in year 2. Utilization of growth promoting implants did not negatively impact postweaning reproductive development or compromise pregnancy rates in beef heifers. Based on these results, administration of a growth promoting Synovex-C implant at 2 mo of age may allow for increased body weight at weaning, without hindering reproductive performance.

Management of beef females during the first year of life can impact fertility and reproductive longevity. Cattle producers can improve calf weight gains by using growth promoting implants; however, to be applicable, they must not negatively impact heifer reproductive performance or development. Understanding the impact of growth promoting implants on growth, fertility, and reproductive development is important to determine if they can be utilized as an effective management strategy in heifers intended to be retained in the breeding herd. To determine if growth promoting implants influence fertility, 233 heifer calves either received no implant, a Synovex-C implant at 2 mo of age, or a Synovex-C implant at 7 mo of age. Implanting heifers at 2 mo of age increased body weight at weaning. Implanting heifers at 7 mo of age did not improve body weight gains. Implanting heifers at 2 or 7 mo of age resulted in similar pregnancy rates. By using a growth promoting implant at 2 mo of age in beef heifers, producers may be able to increase heifer weaning weight without negatively affecting reproductive development or pregnancy rates. Additional body weight at weaning may provide a profit advantage for heifers not retained as replacements.

Understanding intake on pastures: how, why, and a way forward.

An assessment of dietary intake is a critical component of animal nutrition. Consumption of feed resources is the basis upon which feeding strategies and grazing management are based. Yet, as far back as 1948, researchers have lauded the trials and tribulations of estimation of the phenomenon, especially when focused on grazing animals and pasture resources. The grazing environment presents a unique situation in which the feed resource is not provided to the animal but, rather, the animal operates as the mechanism of harvest. Therefore, tools for estimation must be developed, validated, and applied to the scenario. There are a plethora of methods currently in use for the estimation of intake, ranging from manual measurement of herbage disappearance to digital technologies and sensors, each of which come with its share of advantages and disadvantages. In order to more firmly grasp these concepts and provide a discussion on the future of this estimation, the Forages and Pastures Symposium at the 2020 ASAS-CSAS-WSASAS Annual Meeting was dedicated to this topic. This review summarizes the presentations in that symposium and offers further insight into where we have come from and where we are going in the estimation of intake for grazing livestock.

Developmental Resiliency: In Utero Adaption to Environmental Stimuli.

Stimuli experienced in utero can have a lasting impact on livestock growth, reproduction, and performance. Variations in environment, production system, and management strategies lead to discrepancies in the literature regarding how specific treatments influence animal performance. Studies comparing the influence of maternal undernutrition to well-fed counterparts typically result in decreased productivity of offspring. Via adaptation to nutritional or environmental stressors, dams may develop mechanisms to ensure proper nutrient supply to the fetus. It appears nutrient deprivation must be severe for consistent results. Potential mechanisms for altered performance in grazing systems and overnutrition settings are discussed.

The effect of precipitation received during gestation on progeny performance in Bos indicus influenced beef cattle.

The objective of this retrospective study was to determine the effect of precipitation level during key fetal development periods on beef progeny performance. The hypothesis that was precipitation level during different periods of gestation would program subsequent calves for an environment similar to that experienced in utero resulting in altered growth and reproductive performance. Data were collected on Brangus cows (n = 2,429) over a 46-yr span at the Chihuahuan Desert Rangeland Research Center. Recorded precipitation values were used to calculate average precipitation associated with total gestation (April-March), early gestation, (July-September), and late gestation (December-February). These values were used to classify treatments: low (z value ≤ -1.00), average (z value -0.99 to +0.99), and high (z value ≥ +1.00) for each time period. Calves experiencing high precipitation throughout gestation had heavier body weight (BW) at birth (P = 0.02), weaning (P = 0.05), and adjusted 205-d BW (P = 0.04) than those experiencing low precipitation . Female progeny gestated during low precipitation throughout gestation were more likely to remain (P < 0.0001) in the herd and calve after the age of 8 yr when compared to heifers experiencing high precipitation levels in utero (38% vs. 16% ± 5%, respectively). In addition, a greater percentage (P < 0.0001) of heifers experiencing low precipitation levels during the early gestation period produced a calf within the herd after 8 yr of age. Similarly, calves experiencing low precipitation during those same time points also had a greater number of calves while in production (P < 0.0001) when compared to the average and high precipitation groups. These results indicate that selection of heifers exposed to lower than average precipitation levels in utero may result in increased herd retention and productivity.

BEEF SPECIES-RUMINANT NUTRITION CACTUS BEEF SYMPOSIUM: Influence of management decisions during heifer development on enhancing reproductive success and cow longevity1.

Profitability of beef cattle producers can be directly tied to the productive lifespan of a cow. Management decisions influencing heifer nutrition and reproduction play a key role in establishing heifer fertility and longevity. Altering feeding strategies to utilize compensatory growth has been reported to have a positive influence on fertility during the first breeding season; however, there are discrepancies in the literature as to the impact this strategy may have on the proportion of heifers attaining puberty prior to entering their first breeding season. Ultimately, this may affect lifetime productivity as heifers born early in the calving season produce more kilograms of weaned calf over their first 6 calves, as well as, remain in the herd longer than those animals born later in the calving season. Thus, incorporation of reproductive technologies to identify fertile animals or aid in improving conception earlier in the breeding season may improve heifer reproductive performance and longevity. Reproductive tract scores have been utilized to identify animals which are more reproductively mature, increasing the likelihood of successful artificial insemination. Antral follicle counts (AFC), which predict the number of follicles in the ovarian reserve, have not only been reported to have a moderate to high heritability, but have also been used to identify animals with greater reproductive potential. Beef heifers classified as high AFC have greater pregnancy rates and longevity than low AFC heifers. Additionally, maternal diet may play a role in influencing reproductive success and ultimately cow longevity. Improving maternal plane of nutrition has been reported to increase female offspring pregnancy rates. Overall, recent research has provided producers with a variety of methods to optimize animal performance while enhancing reproductive success and longevity to ensure profitability.

Growth and Reproductive Performance of Rangeland Beef-Cattle as Influenced by Controlled and Uncontrolled Populations of Horn Flies (Diptera: Muscidae).

A 4-yr study was conducted on native rangeland to assess the growth and reproductive performance of cows (Bos taurus) infested with naturally occurring seasonal populations of horn flies (Haematobia irritans). One hundred five Angus × Hereford cow-calf pairs were evaluated as a randomized complete block that was replicated across 4 yr. Cows were approximately 39 d postpartum at the beginning of each yearly trial and were randomly allocated to either an untreated control (UTC) or an insecticide-treated (TRT) herd. Horn fly populations were monitored throughout each yearly replication and blood serum progesterone levels were used to estimate postpartum interval lengths and days to pregnancy. Initial body weights of cows were collected in May with final body weights and calf weaning weights acquired in October of each year. Monthly horn fly control ranged from 85.55 to 99.57% throughout the 4 yr. Cows within UTC herds maintained on average 530.10 ± 94.74 more (P = 0.0015) flies per animal than TRT. However, no differences were detected between treatment groups for any of the reproductive parameters evaluated (P > 0.05). Despite a lack of difference in the reproductive parameters measured, TRT cows gained more (P = 0.0492) weight throughout the fly seasons when compared to UTC cattle. Furthermore, calves paired with insecticide-treated cows tended (P = 0.0680) to wean 16.28 ± 8.04 kg heavier than calves paired with cows exposed to naturally occurring horn fly populations.

Substituting ground woody plants for cottonseed hulls in kid goat feedlot diets: growth performance and blood serum chemistry.

Boer × Spanish kid goats (n = 48) were used to evaluate effects of using ground woody products in feedlot diets on growth performance and blood serum chemistry. A completely randomized study design was used with 2 feeding periods (Period 1 = 70% concentrate, days 0 to 26; Period 2 = 86% concentrate, days 27 to 64). Goats were individually fed 1 of 6 diets that differed only by roughage source (n = 4 wether males and 4 females/treatment; initial BW = 22 ± 2 kg): cottonseed hulls (CSH; control) or ground wood consisting of redberry (RED), blueberry (BLUE), one-seed (ONE), or eastern red cedar (ERC) Juniperus spp., or Prosopis glandulosa (MESQ). Ground woody diets were individually compared with CSH. During Period 1, goats fed CSH had greater (P < 0.05) average daily DMI (DMI), ADG, and G:F than goats fed MESQ and tended to have greater (P < 0.10) ADG and G:F than goats fed BLUE. A Treatment × d interaction (P = 0.008) was observed for goat BW during Period 1 and goats fed CSH tended (P < 0.09) to have greater BW on day 27 than goats fed BLUE or MESQ. During Period 2, Treatment × d interactions were not observed (P > 0.29) for DMI, ADG, G:F, or BW and no differences were observed between goats fed CSH and goats fed any of the treatment diets. Various blood serum variables were different between CSH and goats fed diets containing woody plants (mainly during Period 1); however, blood serum profiles did not indicate hepatotoxicity or any other health issue. Collectively, results suggested that ground Juniperus pinchotii, Juniperus ashei, or Juniperus monosperma can completely replace CSH in goat feedlot diets without negatively affecting growth performance or animal health. During Period 1, feeding diets to goats that contain 30% Juniperus virginiana (ERC) or P. glandulosa (MESQ) may not be economically justifiable in most scenarios, even though goat health, assessed by blood serum profiles, was not negatively affected. However, using 14% J. virginiana (ERC) or P. glandulosa (MESQ) in finishing diets is warranted.

Effect of feeding flax or linseed meal on progesterone clearance rate in ovariectomized ewes.

Ovariectomized ewes (n=22; 68.76+/-2.34 kg initial body weight; 2.9+/-0.1 initial body condition score) were individually fed one of three diets: (1) control (phytoestrogen-free; n=7), (2) flax containing diet (n=8), or (3) linseed meal (LSM) containing diet (n=7) to investigate the rate of progesterone (P4) clearance. On day 20 of feeding (day 0=initiation of treatment), a P4 releasing device (CIDR) was placed in the vagina and jugular blood samples were obtained prior to CIDR insertion and 15, 30, 60, and 120 min following CIDR insertion. Further, blood samples were obtained daily between days 21 and 24. On day 25, blood samples were retrieved prior to CIDR removal and 2, 5, 10, 15, 30, 60, 120, and 360 min following CIDR removal. There was no difference in initial or final body weight or body condition score and there were no time by diet interactions on P4 clearance. The fractional rate of P4 uptake measured prior to CIDR insertion through day 4 following insertion tended to be greater (P=0.07) in LSM fed ewes (508.75+/-71.37%/min) compared to flax (295.39+/-66.76%/min) and control fed (287.54+/-71.37%/min) ewes. Diet tended (P=0.10) to influence P4 clearance rate when measured from prior to CIDR removal through 120 min following CIDR removal with LSM fed ewes having a greater (1.26+/-0.2) fractional rate constant than flax (0.929+/-0.09) and control fed (0.922+/-0.09) ewes. Flax fed ewes also had more (P<0.01) omega-3 fatty acids and total fatty acids in plasma. Reports of increased pregnancy rates in dairy cows fed flax may relate to P4 metabolism.