Effect of human somatotropin-releasing factor and photoperiods on carcass parameters and mammary gland development of dairy heifers.
Forty-eight heifers (3 mo old) were subjected for 35 wk to twice daily s.c. injections of saline or human somatotropin-releasing factor (5 microgram.kg-1 BW) and photoperiod of 8 h (short day) or 16 h (long day) of light daily according to a 2 X 2 factorial design. There was no treatment effect on slaughter weight, withers height, and carcass length. Somatotropin-releasing factor increased thymus weight, metacarpal length, and protein content of the carcass but decreased carcass fat content. Long day photoperiod increased chest girth, pituitary weight, and carcass yield. Effects of somatotropin-releasing factor and photoperiod were not additive on volume of mammary parenchymal tissue; there was also a treatment interaction on liver and lung weights. However, extraparenchymal mammary tissue was decreased by human somatotropin-releasing factor and short day photoperiod. In conclusion, use of somatotropin-releasing factor and photoperiod treatments affected carcass parameters and composition and mammary growth.
Ringuet
H
H
Agriculture Canada Research Station, Lennoxville, Quebec, Canada.
Petitclerc
D
D
Sorensen
M T
MT
Gaudreau
P
P
Pelletier
G
G
Morisset
J
J
Couture
Y
Y
Brazeau
P
P
D000818:Animals; D001823:Body Composition / Q000187:drug effects; D001835:Body Weight / Q000187:drug effects; D002417:Cattle / Q000254:growth & development*; D002940:Circadian Rhythm; D005260:Female; D013007:Growth Hormone-Releasing Hormone / Q000494:pharmacology*; D008027:Light; D008099:Liver / Q000187:drug effects / Q000254:growth & development; D008168:Lung / Q000187:drug effects / Q000254:growth & development; D008321:Mammary Glands, Animal / Q000187:drug effects / Q000254:growth & development*; D009929:Organ Size / Q000187:drug effects; D010902:Pituitary Gland / Q000187:drug effects / Q000254:growth & development; D013950:Thymus Gland / Q000187:drug effects / Q000254:growth & development; D014057:Tomography, X-Ray Computed / Q000662:veterinary
D013007:Growth Hormone-Releasing Hormone