Energy and protein as nutritional drivers of lactation and calf growth of farmed red deer

Red deer calf growth rates from birth to 12weeks of age seldom exceed 450g/day on the best quality ryegrass/white clover pastures offered to lactating hinds over summer. However, the genetic potential for calf growth exceeds that observed on most farms. The metabolisable energy (ME) content of feed is traditionally used as the measure of feed quality for lactating hinds. The present study investigated the possibility that protein, rather than energy, content of forage may be a more important determinant of hind lactation performance and calf growth for red deer. A total of 16 mature red deer hinds pregnant to a red deer stag were calved indoors in individual pens. For the duration of their 12-week lactation they were each given daily ad libitum offers of pellet ration (+5% by weight of lucerne hay) that contained either low energy/low protein (LE/LP), low energy/high protein (LE/HP), high energy/low protein (HE/LP) or high energy/high protein (HE/HP) (i.e. n=4 per treatment). Calves and hinds were weighed weekly during the study. The mean dry matter intake of hinds was significantly higher (by about 35–40%) for hinds receiving low energy rations (i.e. LE/LP and LE/HP groups) irrespective of protein content. This resulted in all treatment groups exhibiting the same average energy intake, providing strong evidence for ‘energy balancing’ of feed intake (i.e. intake compensates for energy content of feed). As a consequence of “energy balancing” there was substantial between-treatment group variance in mean protein intake (400–1200gcrudeprotein/hind/day). However, there was no relationship between protein intake and calf growth performance. In contrast, regression analysis of individual hind variation in energy intake and calf growth revealed that energy intake during lactation was a major determinant of calf growth performance. Overall, calf growth during the 10–12weeks of lactation was lower than expected within the indoor system, and probably reflects a low intake of pellets by the calves themselves. The results of the study support the concepts of energy maximisation and do not support the central hypothesis of potential protein deficiency. Data from this experiment suggest that 400g/day crude protein intake is adequate for lactation in red deer hinds.