Beef Research News
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The objective of this study was to evaluate the effects of acclimation to handling on growth, plasma concentrations of progesterone (P4) and cortisol, temperament, and reproductive performance of Brahman-crossbred heifers. Over 2 consecutive years, 37 Braford and 43 Brahman x Angus heifers were initially evaluated, within 30 d after weaning, for BW and puberty status via transrectal ultrasonography and plasma P4 concentrations (d 0 and 10), and for temperament by measurements of chute score, pen score, and exit velocity (d 10 only). On d 11, heifers were stratified by breed, puberty status, temperament score, BW, and age and randomly assigned to receive or not (control) the acclimation treatment. Acclimated heifers were exposed to a handling process 3 times weekly (Mondays, Wednesdays, and Fridays) for 4 wk (d 11 to 39 of the experiment). The acclimation treatment was applied individually to heifers by processing them through a handling facility, whereas control heifers remained undisturbed on pasture. Heifer puberty status, evaluated via plasma P4 concentrations and transrectal ultrasonography, and BW were assessed again on d 40 and 50, d 80 and 90, and d 120 and 130. Blood samples collected before (d 10) and at the end of the acclimation period (d 40) were also analyzed for plasma concentrations of cortisol. Heifer temperament was assessed again on d 40 of the study. No interactions containing the effects of treatment, breed, and year were detected. Acclimated heifers had reduced (P < 0.01) ADG compared with control heifers (0.50 vs. 0.58 kg/d, respectively). Attainment of puberty and pregnancy, however, was hastened (P = 0.02 and 0.04, respectively) in acclimated heifers compared with control. Acclimated heifers had reduced chute score (P < 0.01) and concentrations of cortisol (P < 0.01) and P4 (P = 0.03; prepubertal heifers only) compared with control heifers after the acclimation period (1.37 vs. 1.84 for chute score; 37.8 vs. 50.5 ng/mL of cortisol; 0.52 vs. 0.78 ng/mL of P4). Results from this study indicated that, although acclimation to handling decreased ADG, it resulted in decreased chute score, reduced plasma concentrations of cortisol and prepubertal P4, and enhanced reproductive performance of Brahman-crossbred heifers.
R. F. Cooke*, J. D. Arthington2, B. R. Austin, and J. V. Yelich. Effects of acclimation to handling on performance, reproductive, and physiological responses of Brahman-crossbred heifers. J. Anim Sci. 2009. 87:3403-3412.
Early estrus-synchronization protocols focused on regressing the corpus luteum with an injection of prostaglandin F2 (PG) followed by detection of estrus or involved the use of exogenous progestins that prevent estrus from occurring. Later, protocols combining the use of PG and exogenous progestins were developed. Gonadotropin-releasing hormone was utilized to control follicular waves, synchronize ovulation or to luteinize large dominant follicles. Our research aimed to develop reliable protocols that: 1) relied solely on fixed-timed AI (TAI); 2) required a maximum of 3 animal handlings, and 3) were successful in estrous-cycling and noncycling females. In cows, insertion of an intravaginal progesterone insert during the 7-d interval between the initial GnRH and PG injections enhanced pregnancy rates by 9 to 10%. In a multi-location study, a TAI protocol yielded pregnancy rates similar to a protocol involving detection of estrus plus a fixed-time clean-up AI for females not detected in estrus (54 vs. 58%, respectively, for cows and 53 vs. 57%, respectively, for heifers). Initiation of estrous cycles in noncycling cows is likely the primary manner in which beef producers may improve fertility in response to estrus synchronization and TAI protocols. Treatment of noncycling females with progesterone and GnRH increases the percentage of cycling females and improves fertility to a TAI, but inducing cyclicity with hCG failed to enhance fertility in TAI protocols. Supplementing progesterone after TAI failed to increase pregnancy rates in beef cattle. In contrast, administration of hCG 7 d after TAI induced an accessory CL, increased progesterone, and tended to enhance pregnancy rates. Development of TAI protocols that reduce the hassle factors associated with ovulation synchronization and AI provide cattle producers efficient and effective tools for capturing selective genetic traits of economic consequences. Location variables, however, that may include differences in pasture and diet, breed composition, body condition, postpartum interval, climate, and geographic location, affect the success of TAI protocols.
G. C. Lamb*, C. R. Dahlen, J. E. Larson, G. Marquezini* and J. S. Stevenson. Control of the estrous cycle to improve fertility for fixed-time artificial insemination (TAI) in beef cattle: A review. Published online first on September 25, 2009. J. Anim Sci. 1910. doi:10.2527/jas.2009-2349
Developmental programming is the concept that a maternal stimulus or insult at a critical period in fetal development has long-term effects on the offspring. Historically, considerable efforts have been made to understand how nutrition influences health and productivity during the postnatal period. Whereas maternal nutrition during pregnancy plays an essential role in proper fetal and placental development, less is known about how maternal nutrition affects the offspring’s health and productivity. Conceptus growth is sensitive to direct and indirect effects of maternal dietary intake. Even from the earliest stages of embryonic life when nutrient requirements for conceptus growth are negligible, alterations in tissue composition can occur, influencing future growth of the compromised organ system. Not only is neonatal health compromised, but subsequent health may be programmed because offspring from undernourished dams have exhibited poor growth and productivity and developed significant diseases later in life. While the literature is now evolving with increasing evidence of how maternal nutrient restriction impairs several prenatal physiological variables, few studies have evaluated post-natal growth and development in livestock species, and fewer have evaluated it in beef cattle. In addition, very few studies have evaluated restriction of specific components of the diet during pregnancy (such as protein) on offspring growth and performance. This review focuses on how maternal nutrition impacts conceptus growth and postnatal responses in beef cattle.
R. N. Funston, D. M. Larson and K. A. Vonnahme. Impacts of maternal nutrition on conceptus growth and offspring performance: Implications for beef cattle production Published online first on October 9, 2009. J. Anim Sci. 1910. doi:10.2527/jas.2009-2351
Current genetic evaluations are performed separately for each breed. Multiple breed genetic evaluations, however, assume a common base among breeds enabling producers to compare cattle of different breed makeup. Breed and heterosis effects are needed in a multi-breed evaluation because databases maintained by breed associations include few crossbred animals which may not be enough to accurately estimate these effects. The objective of this study was to infer breed effects (BE), maternal effects (ME), direct heterosis effects, and maternal heterosis effects for growth and carcass traits using least square means estimates from crossbreeding studies published in the literature from 1976 to 1996. The dataset was formed by recording each least square mean along with the breed composition, maternal breed composition, and direct and maternal heterozygosity. Each trait was analyzed using a single trait fixed effect model which included study as a fixed effect and breed composition and heterozygosity as covariates. Breed solutions for each trait were expressed relative to the Angus breed. Direct BE for weaning weight ranged from -7.0 ± 0.67 kg (British Dairy) to 29.3 ± 0.74 kg (Simmental) and ME ranged from -11.7 ± 0.24 kg (Hereford) to 31.1 ± 2.22 kg (Gelbvieh). Direct BE for birth weight ranged from -0.5 ± 0.14 kg (British Dairy) to 10.1 ± 0.46 kg (Continental Beef) and ME ranged from -7.2 ± 0.13 kg (Brahman) to 6.0 ± 1.07 kg (Continental Beef). Direct BE ranged from -17.9 ± 1.64 kg (Brahman) to 21.6 ± 1.95 kg (Charolais), from -6.5 ± 1.29 kg (Brahman) to 55.8 ± 1.47 kg (Continental Beef), from -8.1 ± 0.48 cm2 (Shorthorn) to 21.0 ± 0.48 cm2 (Continental Beef), and from -1.1 ± 0.02 cm (Continental Beef) to 0 ± 0.00 cm (Angus) for post weaning gain, carcass weight, rib eye area, and fat thickness, respectively. The use of literature estimates to predict direct and maternal breed and heterosis effects may supplement their direct prediction in a multi-breed evaluation.
J. L. Williams, I. Aguilar, R. Rekaya and J. K. Bertrand. Estimation of breed and heterosis effects for growth and carcass traits in cattle using published crossbreeding studies. Published online first on October 9, 2009. J. Anim Sci. 1910. doi:10.2527/jas.2008-1628
The influences of nutritional protein and energy during early and mid pregnancy on milk production and postpartum reproductive parameters were determined in 70 beef heifers of two composite breeds (Bos indicus X Bos taurus). At artificial insemination (AI), heifers were divided into four dietary treatment groups identified by the level of protein, and to a lesser extent energy, fed during the first and second trimesters: high/high (HH), high/low (HL), low/high (LH), and low/low (LL). Milk production was lower in the heifers receiving high treatment in first trimester than that in heifers receiving the low treatment (P=0.01). Milk production was negatively associated with dam body condition score (BCS; P=0.01), nonesterified fatty acids (P=0.001), and leptin (P=0.02) and positively associated with urea (P<0.001) concentrations during lactation. Increased dietary protein in the first trimester increased or decreased concentrations of colostral protein dependent upon genotype (P=0.03). Colostral protein was positively associated with bovine pregnancy associated glycoprotein from late gestation (P=0.007). Milk fat was negatively associated with BCS (P=0.007) and influenced by genotype (P=0.003). Dietary treatment did not affect the postpartum reproductive performance of beef heifers. Gestation length (P<0.001) and the postpartum interval to first estrus (PPI; P=0.02) were positively associated with calf size. Placental size was negatively associated with placental expulsion time (P<0.01). Prepartum BCS of the heifers was negatively associated with PPI (P=0.01). Overall, high levels of nutrition during early gestation are detrimental to milk production in beef heifers.
T.M. Sullivan, G.C. Micke, V.E.A. Perry. Influences of diet during gestation on potential postpartum reproductive performance and milk production of beef heifers. Theriogenology Volume 72, Issue 9, Pages 1202-1214 (December 2009)