Voluntary food intake of pregnant and non-pregnant red deer hinds during the gestating period

Abstract

Efficient venison production systems rely in New Zealand on maximal growth of deer calves before their first winter. This is facilitated by earlier calving (i.e. March conception for October/November calving). However, previous research has shown that hinds conceiving early in the breeding season have a longer gestation length than those conceiving later, negating some of the gains of achieving early conception. It is hypothesised that a moderate energy imbalance during the last trimester of pregnancy influences fetal growth trajectory resulting in variation of gestation length. While young red deer, adult stags and non-pregnant hinds exhibit a photoperiod-mediated reduction in voluntary food intake (VFI) during winter, it is not known if this occurs in pregnant hinds. Such a decrease in VFI would exacerbate a moderate energy imbalance during the third trimester of pregnancy. The objective of this study was to test the hypothesis that pregnancy status does not affect the photoperiod-mediated reduction in VFI of red deer hinds during winter. Seven pregnant (P) and seven non-pregnant (NP) hinds were housed indoors in individual pens from April to November where they were offered daily an ad libitum pelleted ration. Food intake was measured daily and hinds were weighed and body condition scored (BCS) fortnightly. In addition, blood samples were collected at 4-week intervals to determine plasma concentrations of two appetite regulating hormones, leptin and ghrelin. Mean (± SEM) live weight (LW) on 27 April was 117.1 ± 6.0 kg and 124.1 ± 10.3 kg for P and NP hinds, respectively. On average, P hinds gained 74 g/day and NP hinds lost 27 g/day (P < 0.05) in autumn. Mean live weight (LW) of both groups then increased for the remainder of the study with no significant difference between groups during specific time periods. Body condition score (BCS) of both groups increased during autumn and winter (P > 0.05), but whereas BCS of P hinds decreased, that of NP hinds increased in spring (-0.001 BCS units/day vs. 0.006 BCS units/day; P < 0.05). Pregnancy status of the hinds had no significant effect on mean VFI throughout the trial except for the last five days before parturition when VFI of P hinds decreased dramatically (P < 0.001). Mean VFI of both groups was significantly higher about 1 May and 1 November than 1 July (0.72 ± 0.05, 0.69 ± 0.03 and 0.58 ± 0.05 MJME/kg LW respectively; P < 0.05). There was a significant negative correlation of gestation length with mean VFI during the study period (P< 0.05), such that, for every 0.1 MJME/kg LW0.75/day increase in mean VFI, gestation length decreased by 6.4 days. Pregnancy status had no significant effect on plasma concentration of leptin or ghrelin at any of the sampling times (P > 0.05). Circulating leptin concentration was associated significantly (P < 0.01) with BCS, but not VFI. Results from this study support the hypothesis that pregnancy status does not affect the photoperiod-mediated depression in VFI of red deer hinds during winter. It is suggested that to mitigate effects of the observed moderate energy imbalance during the last third of pregnancy, farmers should ensure hinds are in good condition going in to winter and that high quality feed is available throughout gestation.