title: Pre-pubertal measurements of the somatotrophic axis as predictors of milk production in Holstein-Friesian dairy cows.
abstract: This study investigated possible relationships between measurements of the somatotrophic axis in pre-pubertal dairy calves and subsequent milk yields. Endogenous growth hormone (GH) release was measured through a fed and fasted period in fifty 6-month-old Holstein-Friesian heifers and they were then challenged with growth hormone-releasing factor (GRF) to assess their GH release pattern. Insulin-like growth factor-I (IGF-I), insulin and glucose concentrations were measured in relation to time of feeding. Cows were subsequently monitored through their first three lactations to record peak and 305-day milk yields. In the first lactation, milk energy output for the first 120 days of lactation was also calculated. The mean 305-day milk yield increased from 7417 +/- 191 kg in the first lactation (n=37) to 8749 +/- 252 kg in the third (n=25). There were no significant relationships between any measures of GH secretion and peak or 305-day yield in any lactation. A highly significant positive relationship was established between the GH peak measured 10 min post-GRF challenge and 120-day milk energy values in the first lactation. This relationship was, however, only present in the sub-population of 12 cows culled after one or two lactations and was absent in the 25 animals remaining for the third lactation. There were no significant relationships between pre-pubertal IGF-I and fed or fasted insulin or glucose concentrations and any subsequent measurement of yield. The usefulness of GH secretagogue challenges in calves as a predictive test for future milk production is thus limited but may have some bearing on nutrient partitioning and longevity.
authors.affiliation: Reproduction and Development Group, Royal Veterinary College, Hawkshead Lane, Hatfield, Hertfordshire AL9 7TA, UK. v.taylor@imperial.ac.uk
authors.forename: V J
authors.initials: VJ
authors.lastname: Taylor
authors.forename: D E
authors.initials: DE
authors.lastname: Beever
authors.forename: M J
authors.initials: MJ
authors.lastname: Bryant
authors.forename: D C
authors.initials: DC
authors.lastname: Wathes
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002417:Cattle / Q000097:blood / Q000502:physiology*; D005260:Female; D013006:Growth Hormone / Q000097:blood* / Q000378:metabolism; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology; D007328:Insulin / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000032:analysis*; D007774:Lactation / Q000097:blood; D008297:Male; D008892:Milk / Q000378:metabolism*; D011237:Predictive Value of Tests; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D012044:Regression Analysis
chemical_list: D001786:Blood Glucose; D007328:Insulin; D011374:Progesterone; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D013007:Growth Hormone-Releasing Hormone