title: Effect of weaning date (normal vs. late) on performance of young and mature beef cows and their progeny in a fall calving system in the Southern Great Plains.
abstract: Data from 158 predominantly Angus fall-calving beef cows were used in 4 consecutive years to determine the effects of weaning date and cow age class on cow and calf performance. Treatments were arranged in a 2 x 2 factorial with 2 weaning dates and 2 age classes (young cows <or=3 yr and mature cows >or=4 yr). Weaning dates were 1) normal weaning in mid-April at 210 d of age (NW) and 2) late weaning in mid-July at 300 d of age (LW). Mature cows were heavier (P < 0.01) than young cows throughout the trial, although BCS was similar (P >or= 0.10) among cow age classes. Cow BW (P = 0.58) and BCS (P = 0.40) were similar among weaning treatments at NW; however, at the beginning of the calving season, NW cows were heavier (585 vs. 562 kg; P = 0.02) and had greater BCS (6.57 vs. 5.95; P < 0.0001) than LW cows. Postpartum BW and BCS losses were greater (P < 0.0001) for NW cows, resulting in similar BW (P = 0.56) and BCS (P = 0.07) at the beginning of the breeding season and until April. Progeny of NW cows were 2.4 kg heavier (P < 0.01) at birth and grew faster before the April weaning date, resulting in increased BW (8 kg; P < 0.05) at the time of normal weaning. This increase in BW gain may be partially explained by the increased milk production of NW cows (0.59 kg/d as measured in February; P < 0.05). Although NW calves had increased BW in April, LW calves were heavier in July because of increased ADG during the weaning interval (1.13 vs. 0.8 kg; P < 0.0001). A cow age class x weaning date interaction (P = 0.007) was detected for pregnancy rate. Pregnancy rates were greater (P < 0.10) for LW-mature cows (96.7%) and NW-young cows (98.4%) than for LW-young cows (89.3%). However, pregnancy rate of NW-mature cows (90.2%) did not differ (P = 0.12) from that of LW-mature or LW-young cows, but was less than that of NW-young cows. These findings indicate that producers may benefit from matching weaning date to cow age class. It appears more advantageous to delay weaning of calves born to dams 4 yr or older while maintaining NW for dams 3 yr or younger at the time of calving. Late weaning had no detrimental effects on the performance of mature cows.
authors: Department of Animal Science, Oklahoma State University, Stillwater, USA.
authors: M D
authors: MD
authors: Hudson
authors: J P
authors: JP
authors: Banta
authors: D S
authors: DS
authors: Buchanan
authors: D L
authors: DL
authors: Lalman
mesh_terms: D000818:Animals; D001724:Birth Weight; D001835:Body Weight / Q000502:physiology; D002417:Cattle / Q000254:growth & development* / Q000502:physiology; D005260:Female; D007774:Lactation / Q000502:physiology; D008892:Milk / Q000737:chemistry / Q000378:metabolism; D009825:Oklahoma; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D013997:Time Factors; D014886:Weaning