Somatotropic axis and concentrate supplementation in grazing dairy cows of genetically diverse origin

• Published in: Journal of dairy science 2011-01, Vol.94 (1), p.303-315
• Main Authors: Grala, T.M., Lucy, M.C., Phyn, C.V.C., Sheahan, A.J., Lee, J.M., Roche, J.R.
• Format: Article
• Language: English
• Subjects: Animal Nutritional Physiological Phenomena; Animal productions; Animals; Biological and medical sciences; Blood Glucose - analysis; body condition; Body Constitution - physiology; Body Weight - physiology; Cattle - genetics; Cattle - physiology; cow feeding; dairy cows; diet; Dietary Supplements; dose response; early lactation; experimental diets; Fatty Acids, Nonesterified - blood; feed concentrates; feed supplements; Feeding Methods; Feeding. Feeding behavior; Female; Fundamental and applied biological sciences. Psychology; gene expression; genotype; grazing; Growth Hormone - blood; Holstein; Hormones - blood; insulin; Insulin - blood; insulin-like growth factor I; Lactation - physiology; Leptin - blood; metabolites; Milk - secretion; milk yield; New Zealand type; North American type; nutrient partitioning; nutrition-genotype interaction; phenotype; somatotropin; strain differences; supplementation; Terrestrial animal productions; Vertebrates; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.2010-3773

Supplementing pasture-fed dairy cows with concentrates in early lactation was hypothesized to result in an earlier postpartum recoupling of the somatotropic axis in New Zealand (NZ)-type Holstein-Friesian dairy cows than in North American (NA)-type cows. To test this hypothesis, NA (n=30) and NZ (n=30) cows were allocated to 1 of 3 supplementation strategies (0, 3, or 6kg of dry matter concentrate/d) for the first 12 wk of lactation in a completely randomized design and a 2 × 3 factorial arrangement. Production traits and characteristics of the somatotropic axis were studied at phenotypic, hormonal, and gene expression levels. Milk production and plasma metabolite concentrations were measured weekly, and liver was biopsied in wk 1, 4, 8, and 12 postcalving. North American cows produced more milk and displayed a larger degree of somatotropic axis uncoupling than did NZ cows. This was evident in strain differences in body condition score, blood growth hormone, and insulin-like growth factor-1 concentrations, and hepatic expression of growth hormone receptor-1a. No strain × diet interactions were observed for any characteristic of the somatotropic axis at either the blood metabolite or gene expression level; however, blood insulin concentrations during wk 7 to 11 postpartum increased with concentrate supplementation in NZ but not NA cows. These results demonstrate that feeding supplements does not result in an earlier recoupling of the somatotropic axis; however, the greater blood insulin concentrations with concentrate feeding in NZ cows from wk 7 may result in an earlier recoupling in this genetic strain, after the period investigated in this study. Further research is required to understand differences in insulin control between these genetic strains.