The purpose of this study was to investigate the effect of prepartum
and postpartum nutrition on milk production of commercial beef cows.
Forty-three Angus or Angus X Holstein females, ranging in age from 2 to 6
yr, were randomly assigned by age and percentage Holstein within age to
one of two prepartum grazing treatments (PRE). All females, regardless of
PRE, were assigned at calving to receive the same post-calving nutritional
energy. Females were assigned at calving by age, percentage Holstein
within age, prepartum nutritional treatment and calving date to one of two
milking groups. Milk weight (grams), milk composition (fat, protein, lactose,
solids-not-fat, somatic cell count), dam body condition score (1 to 9), dam
body weight, dam backfat thickness, loineye area, calf weaning weight and
postpartum interval to estrus were all evaluated. Milk removal occurred
biweekly by vacuum milking machine after intravenous injection of 20 IU of
oxytocin. Samples were weighed and taken for milk analysis and
determination of milk components. At 76± 10 d post-calving, females were
assigned by age, percentage Holstein within age, prepartum nutritional
treatment, and calving date to receive one of two postpartum nutritional
treatments (POST). Females continued to be milked by machine biweekly
until calves were weaned 199 ± 10 d. Differences in grazing level prior to
calving significantly effected calf birth weights, with dams on the prepartum
restricted grazing being lighter in weight at birth, 36.69 ± .68 and
38.95 ± .81 kg for PRE-L and PRE-H groups, respectively, however grazing
differences did not effect calf weaning weight, calf gain or calf average daily
gain. POST nutritional treatments significantly effected all calf performance
traits with 37.10±.70, 38.54±.88; 196.89±4.9, 213.33±6.2;
159.79±4.8, 174.78±6.0; .809±.024, .888±.030; for birth weight,
weaning weight, calf gain and calf average daily gain from cows on the
POST -M or POST -H nutritional treatments, respectively. Pre-partum
nutrition effected milk production (P < .001) with dams from the PRE-L
grazing group producing less milk, 5622 ± 75 vs 6888 ±80 g. Postpartum
energy also effected milk production with dams on the POST-H energy level
producing more milk than dams from the POST-M group. Percentages of
fat, protein, lactose and solids-not-fat were not different between the
prepartum or postpartum diets (P>. 10). Somatic cell count was negatively
correlated with dam milk production (P< .03). Postpartum interval to estrus
was shorter for the PRE-L group than for the PRE-H, 43 ± 4 vs 53 ± 4 d.
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