Effects of creep feeding and breed composition on growth of heifer calves and milk production of their dams

Abstract

Heifer calves resulting from matings of Angus (A), Hereford (H), or Simmental (S) bulls with A and H cows were used to examine the effects of creep feeding (CREEP) and heifer genotype (CALFBRD; n = 14 AA, 18 HH, 10 AH. 10 HA, 19 SA, 15 SH) on their preweaning average daily gain (ADG) and the milk yield and milk composition of their dams during the 1987 and 1988 grazing seasons. Eight-hour milk yield was estimated by oxytocin-hand milking procedures at 62, 120, and 170 d from the beginning of the calving season. Dependent variables used in repeated measures analyses included heifer calf and cow ADG between consecutive sampling times, 8-h milk yield (MILK), milk composition (grams per 8 h and percent of fat, protein, and lactose in each sample (FATG, FAT%, PROTG, PROT%, LACTG, LACT%, respectively), fat-corrected milk (FCM) and solid-corrected milk (SCM) from each cow at each sampling time. Neither CREEP nor CALFBRD had any effect on any milk yield or milk composition variable except a slight effect of CALFBRD on LACT%. Year differences were found for cow ADG, FATG, FAT%, PROTG, PROT%, LACT%, FCM and SCM, but not for LACTG, MILK or calf ADG. Differences (P≤ 0.001) in calf ADG due to CREEP and CALFBRD were found. Age of cow was a significant source of variation for cow and calf ADG and all milk yield variables, but not for FAT%, PROT%, or LACT%. Time trends (within subject factors) were significant for all dependent variables. Time by Year effects were important for cow and calf ADG, MILK, SCM, PROTG, PROT%, and LACTG. Both the breed composition of calves and supplementation with creep feed influenced calf gains but had no effect on their dam's milk yield, milk composition, or changes in body weight. Key words: Beef cattle, creep feeding, milk yield, milk composition, average daily gain, repeated measurements