Thermoregulatory differences in lactating dairy cattle classed as efficient or inefficient based on residual feed intake

Abstract

It is suggested that one-third of the inter-animal differences in efficiency is explained by differences in digestion, heat production, body composition and activity; while the remaining variation is the result of energy expenditure due to biological processes such as ion pumps and mitochondrial function. Inefficient animals may be wasting energy on inefficient processes resulting in increased heat production that may be reflected by differences in skin and core temperature. While the association between heat production and residual feed intake (RFI) has been touched on, it is yet to be fully elucidated. It is hypothesised that more efficient animals will expend less energy as heat, which will be reflected by differences in core and skin temperature measures. Fifty-four primiparous, Holstein-Friesian cows previously assessed for RFI (26 inefficient/high RFI, 28 efficient/low RFI) were selected and drafted into outdoor holding yards for measurements on two occasions (once during lactation and once during the non-lactating ‘dry’ period). Measures of body temperature were obtained using an infrared (IR) camera to obtain skin (surface) temperatures at multiple locations [muzzle, eye, jaw, ear, leg (front and back), rump, shoulder, teat, udder, side and tail] and rectal temperatures were measured using a digital thermometer. Respiration rates (RR) were obtained by counting the number of flank movements in 1 min. A subset of 16 cows (8 efficient and 8 inefficient) were utilised for further IR imagery in an undercover environment (to eliminate the influences of external environments). Skin temperature measurement obtained using an IR camera during the outdoor period demonstrated that inefficient cows had higher (0.65°C) teat temperatures (P = 0.05). Rectal temperature and RR were not influenced by efficiency group. When IR images were obtained undercover inefficient cows tended to have higher shoulder (0.85°C) and neck (0.98°C) temperatures than efficient cows (P < 0.087); while udder temperature was significantly greater (1.61°C) for inefficient than efficient cows (P = 0.018). These data indicate that some of the differences in efficiency may be attributed to differences in thermoregulation, as reflected by differences in skin (but not core) temperature and that IR imagery is a suitable method for determining these differences in a non-invasive manner. Further research is required to further establish these relationships, and the measurement of skin temperatures should be undertaken indoors to eliminate external environmental influences.