Prepartum Nutrition, Plasma Constituents and Reproductive Performance of Range Beef Cows

Mature pregnant Hereford cows were used to determine the effect of supplemental feed on concentrations of protein, glucose and non-esterified fatty acids (NEFA) in blood plasma, hematocrit in blood and reproductive performance. About 120 days before calving (November 10), 48 cows were assigned to low supplementation (L) so that they would lose approximately 10% of their fall weight by calving and 18 cows were fed moderate supplementation (M) to maintain their weiqht. Low cows were divided into three groups about 60 days before calvinq (nutritional change): one group (n=l9) remained on the low plane of nutrition (LL). Another one-third (n=l9) of the low cows were fed moderate supplementation (LM). The remaining one-third (n=20) of the cows were fed 166% of the moderate supplementation (LH). After calving, all cows received a moderate level of nutrition. Body weight and body condition scores (BCS) were taken from November 10 until April 29, and plasma samples were collected every two weeks during the last 60 days of gestation. Progesterone was quantified in plasma between 15 to 85 days postpartum to determine onset of ovarian activity.Animal Scienc