Effect of Plane of Nutrition Before and During Gestation on the Concentration of Hormones in Dairy Heifers

¹ Department of Animal Science, McGill University, Macdonald Campus, 21,111 Lakeshore Road, Ste. Anne de Bellevue, PQ, Canada H9X 1C0
² Agriculture Canada Research Station, Lennoxville, PQ, Canada J1M 123

Forty heifers (1 yr of age; 313 ± 27 kg of BW) were assigned to one of four treatments in a 2 x 2 factorial design. Main effects were plane of nutrition (ad libitum vs. moderate feeding) during the second isometric phase (1 yr of age to 3 mo of gestation) and during the second allometric phase (3 mo of gestation to 14 d before calving) of mammary development. Jugular blood samples were collected from 16 heifers before the onset of treatment, at the end of the isometric phase, and at the end of the allometric phase. Additional daily blood samples were collected from 32 heifers from 14 d before expected calving to 10 d postpartum and then thrice weekly until 70 d postpartum. High plane of nutrition reduced average growth hormone concentrations during the isometric and allometric phases. Serum concentrations of prolactin tended to be higher in heifers on ad libitum intake during the isometric phase and were higher during the allometric phase. Prolactin was positively correlated with BW and average daily gain during allometric phase. Plasma IGF-I concentrations were not affected by plane of nutrition. No effect was found for previous plane of nutrition on concentrations of growth hormone, prolactin, IGF-I, and progesterone during either prepartum or postpartum periods. Average postpartum IGF-I concentrations were negatively correlated with milk production. A positive relationship existed between mean postpartum concentrations of growth hormone and both peak milk production and feed intake during lactation.

Key Words: plane of nutrition • prolactin • growth hormone • insulin-like growth factor-1

Submitted on May 13, 1993
Accepted on September 27, 1993

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