Beef Research News
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Effect of number of cows in estrus on estrous behavior in cows. Mature Angus and Angus x Hereford cows were used to determine the effects of confinement area and number of cows in estrus on estrous behavior. During each of 2 replicates, 32 nonpregnant, nonlactating cows were maintained in a drylot (60 x 100 m) or in a pasture (12 ha). Estrous cycles were synchronized with 2 injections of PGF2 10 to 14 d apart at the initiation of the experiment. Thereafter, PGF2 was administered between d 6 and 18 of the estrous cycle so that 1, 2 to 3, 4 to 6, or 7 cows were in estrus at the same time. Concentrations of progesterone were quantified in plasma at treatment to ensure cows had a normal response to PGF2 . Duration of estrus and the number of mounts received during estrus were recorded by HeatWatch. If any part of estrus for a cow occurred at the same time as estrus for another cow, the cow was considered to have concurrent estrus with the other cow. Cows in the drylot had a shorter (P < 0.02; 61.8 ± 3.1 h) interval to estrus after PGF2 compared with cows on pasture (72.8 ± 3.3 h). The interval to estrus was longer (P < 0.07) when cows were treated with PGF2 on d 10 to 13 (76.7 ± 3.3 h) of the estrous cycle than when treated on d 6 to 9 (62.3 ± 4.7 h) or d 14 to 18 (62.9 ± 3.6 h). Increasing the number of cows concurrently in estrus increased the number of mounts each cow received per estrus (P < 0.001) and the duration of estrus (P < .01). When only 1 cow was in estrus, she received 11.0 ± 6.2 mounts during 11.6 ± 1.5 h. When 7 cows were in estrus at the same time, each cow received 50.4 ± 3.2 mounts during 17.3 ± 0.8 h. Cows in drylot were in estrus longer (P < 0.04; 16.4 ± 0.8 h) than cows on pasture (14.2 ± 0.7 h). Duration of the longest interval between mounts received decreased (P < 0.002) as the number of cows in estrus at one time increased (5.3 ± 0.7 h for 1 estrous cow; 2.6 ± 0.3 h when 7 cows were in estrus). We conclude that increasing the number of beef cows in estrus at the same time will increase the number of times a cow is mounted and the duration of estrus. The increase in estrous behavior associated with more cows in estrus could increase the number of estrous cows detected with infrequent visual observation.
Floyd, L.N., C. A. Lents, F. J. White and R. P. Wettemann Effect of number of cows in estrus and confinement area on estrous behavior of beef cows. J. Anim Sci. 2009. 87:1998-2004. doi:10.2527/jas.2008-1380
Relationship of incoming traits with carcass and feedlot performance
Steers (n = 15,631) and heifers (n = 5,897) fed at 18 feedlots (total confinement, partial confinement, or open lots) in southwest Iowa between 2002 and 2006 as part of the Tri-County Steer Carcass Futurity sponsored by Iowa State University were used to correlate various phenotypic traits with feedlot performance and carcass traits. Dependent variables (ADG, respiratory morbidity, HCW, fat thickness, calculated yield grade, marbling score, presence or absence of lung damage, loin muscle area (LMA), and LMA*100/HCW) were evaluated on the basis of various phenotypic traits (initial BW, disposition score [1 = calm, 6 = extremely excitable], muscle score, frame score, BCS, number of treatments for respiratory disease, presence of lung lesions, breed makeup, and percentage Angus genetics). Subjectively evaluated phenotypic traits were evaluated by either Iowa State University or USDA personnel. Cattle with greater disposition score (more excitable) had lower initial BW, final BW, ADG, HCW, yield grade, quality grade, marbling score, and mortality (P < 0.01). Respiratory morbidity was negatively correlated with initial BW, ADG, yield grade, HCW, and marbling score (P < 0.01). As initial BW increased, final BW and HCW increased and respiratory morbidity decreased (P < 0.01). Cattle with greater BCS on arrival had greater initial BW but were lighter at harvest (P < 0.01). Increased number of treatments for respiratory disease was associated with lower ADG, greater mortality rate, and greater incidence of lung lesions (P < 0.01). Gain was similar between English- and Continental-breed cattle (P > 0.05), although final BW and HCW were greater and yield grade and yield grade-adjusted marbling score were lower for Continental-breed cattle (P < 0.01). Cattle with a poorer muscling score had lower HCW and LMA and greater yield grade, marbling score, and quality grade (P < 0.01). Animal disposition, health, breed type, and frame score have dramatic effects on live feedlot performance and carcass traits.
Reinhardt, C.D., W. D. Busby and L. R. Corah. Relationship of various incoming cattle traits with feedlot performance and carcass traits. 2009. J. Anim Sci. 1910. doi:10.2527/jas.2008-1293
Heifer reproductive performance and feeding program
Reproductive performance was evaluated in composite heifers born over a 3-yr period that were randomly assigned to control (fed to appetite; n = 205) or restricted (fed at 80% of that consumed by controls adjusted to a common BW basis; n = 192) feeding for a 140-d period, beginning about 2 mo after weaning at 6 mo of age and ending at about 12.5 mo of age. Heifers were fed a diet of 67% corn silage, 18% alfalfa and 9% of a protein-mineral supplement (DM basis). Restricted heifers consumed 27% less feed over the 140 d and had lower ADG (0.53 ± 0.01 vs. 0.65 ± 0.01 kg/d; P < 0.001) than control heifers. After 140 d, all heifers were placed in common pens and subjected to an estrous synchronization protocol to facilitate artificial insemination at about 14 mo of age. Heifers were then exposed to bulls for the remainder of a 51-d breeding season. Average BW of heifers diverged within 28-d after initiation of feed restriction, and differences (P < 0.001) persisted through the prebreeding period (309 ± 1 vs. 326 ± 1 kg at approximately 13.5 mo of age) and subsequent grazing season (410 ± 2 vs. 418 ± 2 kg at about 19.5 mo of age). From end of the 140-d restriction at about 12.5 to 19.5 mo of age, ADG was greater (P < 0.001) in restricted heifers than control heifers (0.51 ± 0.01 vs. 0.47 ± 0.01 kg/d). Proportion of heifers attaining puberty by 14 mo of age tended to be less (P = 0.1) in restricted (60 ± 3%) than control fed heifers (68 ± 3%). Mean BW at puberty was less (P < 0.01) in restricted (309 kg) than control (327 kg) heifers. Pregnancy rate from AI tended to be less (P = 0.08) in restricted (48 ± 4%) than control heifers (57 ± 3%). Proportion pubertal at breeding and pregnant from AI were positively associated (P < 0.1) with heifer age and ADG from birth to start of study. Final pregnancy rates were 87 and 91% for restricted and control heifers, respectively (P = 0.27). Day of breeding season that conception occurred was negatively associated with ADG from birth to weaning (P = 0.005), but was not associated with ADG within treatment (P = 0.60). Economic analysis revealed a $33 reduction in cost to produce a pregnant heifer under the restricted protocol when accounting for pregnancy rates and differences in BW and market prices between selection at weaning and marketing as open heifers at l.5 yr age. A potential economic advantage exists for rearing replacement heifers on a restricted level of feeding during the postweaning period.
A. J. Roberts, T. W. Geary, E. E. Grings, R. C. Waterman and M. D. MacNeil . Reproductive performance of heifers offered ad libitum or restricted access to feed for a 140-d period after weaning. Published online first on May 22, 2009 J. Anim Sci. 1910.
Effects of on-arrival vs. delayed vaccine in beef calves
Stress, commonly associated with weaning, marketing, and shipment of feeder cattle, can compromise immune function, and vaccine administration during immunosuppression may reduce vaccine efficacy and calf growth. Four treatments were compared in a 2 x 2 factorial arrangement to evaluate the effect of on-arrival (d 0) vs. delayed (d 14) administration of clostridial (CLOS) and respiratory (RESP) vaccines on health, performance, bovine viral diarrhea virus (BVDV) antibody titers, and physiological immune measurements of high-risk, newly received calves. Crossbred bull and steer calves (n = 263) were weighed (239 ± 1.2 kg), stratified by sex, and randomly assigned to vaccination treatment: 1) arrival CLOS, arrival RESP (ACAR); 2) arrival CLOS, delayed RESP (ACDR); 3) delayed CLOS, arrival RESP (DCAR); and 4) delayed CLOS, delayed RESP (DCDR). Body weight and blood samples were collected on d 0, 14, 28, 42, and 56. Average daily gain did not differ (P 0.34), averaging 0.98, 0.93, 0.95, and 0.91 kg/d for ACAR, ACDR, DCAR, and DCDR, respectively, for the entire 56-d trial. Vaccination timing did not affect morbidity (P 0.23); however, there tended to be a CLOS timing effect (P = 0.07) and RESP timing effect (P = 0.09) on days to initial bovine respiratory disease (BRD) treatment. Average days to initial BRD treatment were less for ACAR (6 ± 0.8 d) compared with DCDR (8 ± 0.8 d; P = 0.01). Greater white blood cell counts were observed for DCDR than ACDR (P = 0.01), with ACAR and DCAR being intermediate. Serum cortisol concentrations were greater on d 0 than d 14 (P < 0.01) or d 28 (P = 0.01) but no treatment x day interaction (P = 0.21) was observed. Timing of RESP administration affected (P = 0.001) serum BVDV type I titers, with greater (P < 0.01) levels in calves receiving RESP vaccine on arrival. Delaying CLOS or RESP vaccination did not affect BW gain or morbidity in high risk, newly received stocker calves. Calves administered RESP vaccine on d 0 developed antibody titers to BVDV type I earlier than delayed RESP treatments. Total white blood cell count was greatest when RESP and CLOS vaccination were delayed (DCDR).
Richeson, J.T., E. B. Kegley, M. S. Gadberry, P. A. Beck, J. G. Powell and C. A. Jones. Effects of on-arrival versus delayed clostridial or modified live respiratory vaccinations on health, performance, bovine viral diarrhea virus type I titers, and stress and immune measures of newly received beef calves J. Anim Sci. 2009. 87:2409-2418.
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