This study was designed to determine the effects of feed restriction and monopropylene glycol (MPG) supplementation on the reproductive, milk production, and somatotropic axes in dairy heifers postpartum. At calving, 49 Holstein-Friesian heifers were allowed either unrestricted (UNR; n = 18) or restricted access to pasture with (RES+MPG; n = 13) or without (RES; n = 18) MPG supplementation (250 mL drenched twice daily for 150 d). The average body condition score (BCS) of the heifers was 5.3 +/- 0.2 on a scale from 1 to 10 (where 1 = emaciated and 10 = obese). Body condition score and body weight were similar among the groups at calving and decreased after calving for all groups. However, body weight loss was around 10% greater for the RES and RES+MPG groups from wk 3 to 12 compared with UNR group. The length of the postpartum anestrous interval was similar for all groups (47, 51, and 45 +/- 5 d for the UNR, RES, and RES+MPG, respectively). Average milk production, protein, fat, and lactose yields during the first 12 wk postpartum were greater in the UNR group than in the RES and RES+MPG groups. Feed restriction affected plasma concentrations of insulin, with lower concentrations in the RES group compared with the UNR group. There were no differences in plasma concentrations of insulin between the RES+MPG group and the UNR or RES groups. An effect of feed restriction was observed on insulin-like growth factor-I concentrations and also a treatment by time interaction with a changing pattern through time as concentrations in the UNR group increased relative to the RES and RES+MPG groups. There were no differences in growth hormone concentrations among the groups. Glucose concentrations were lower in the RES group when compared with RES+MPG and UNR groups and this difference lessened over time. Plasma concentrations of nonesterified fatty acids were greater in the RES group compared with the RES+MPG and UNR groups. Leptin concentrations in the UNR group were greater than in the RES and RES+MPG groups. Hepatic growth hormone receptor 1A, total growth hormone receptor, and insulin-like growth factor-I relative mRNA expressions decreased postpartum with no effect of feed restriction, MPG supplementation, or interaction between time and treatment. During a challenge with MPG, insulin secretion was stimulated but no effect on postpartum anestrous interval in the treatment groups was observed. It was concluded that restricted pasture availability postpartum in dairy heifers calving in optimal BCS had no effect on the postpartum anestrous interval. It did however decrease milk production; thus, we can infer that monopropylene glycol supplementation does not act to prevent loss of milk yield.
In domestic juvenile chickens kept on short days, photoinduced luteinsing hormone (LH) release, and by inference gonadotrophin-releasing hormone (GnRH) release, are readily detectable within 4 days of photostimulation.2 The molecular mechanisms responsible for the rapid photoinduced release of LH and GnRH in avian species are unknown. It has been suggested that it might involve a cascade of gene expression associated with an increase in cfos in the basal hypothalamus and glial cells in the median eminence.1 A microarray was made consisting of known genes of interest and clones obtained from a hypothalamic short day/long day subtractive library. An experiment was undertaken to determine if this reproductive neuroendocrine microarray could detect new targets for study in the chicken model of photostimulated GnRH release. The microarray was interrogated with hypothalamic RNA from juvenile chickens showing an increase in plasma LH after 4 days of photostimulation. Six genes were identified as showing changes in expression after photostimulation on the microarray. However, only one gene, encoding heat shock protein 108 (HSP108), could be confirmed by quantitative competitive RT-PCR. The expression of this gene decreased both in the hypothalamus and the optic tectum. Treatment of short day juvenile chickens with thyroxine, to mimic the effects of photostimulation, resulted in LH release and depression of HSP108 expression in the anterior but not the basal hypothalamus. Immunocytochemical analyses showed that HSP108 is widely distributed in the brain including glial-like cells with terminals in the median eminence. HSP108 is suggested as a candidate protein involved in the regulation of gonadotrophin release from the median eminence by glial cells. (1)Meddle SL and Follett BK (1995) Photoperiodic activation of fos-like immunoreactive protein in neurones within the tuberal hypothalamus of Japanese quail. Journal of Comparative Physiology [A] 176(1), 79–89.(2)Sreekumar KP and Sharp PJ (1998) Ontogeny of the photoperiodic control of prolactin and luteinizing hormone secretion in male and female bantams (Gallus domesticus). General and Comparative Endocrinology 109(1), 69–74.
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