Long-term undernutritional stress is often a feature of sheep and beef cattle production, but has only become a major feature of dairy cattle husbandry in the United Kingdom in recent winters when food was short and expensive. An experiment was carried out to study the effects of long-term underfeeding during pregnancy and early lactation on some blood constituents, milk yield and composition and body weight of dairy cattle. Two groups of cattle were fed at 60 and 40% of the estimated requirements for maintenance and pregnancy or lactation for 13 weeks before and 13 weeks after calving, and one group was fed at the maintenance level only for the same period. A control group was fed at 100% of estimated requirements for this period. All groups were subsequently fed at the control level for a further 24 weeks.
The experiment showed that cows undergoing long-term nutritional deprivation were able to maintain concentrations of blood constituents within narrow limits; the concentrations of such constituents as glucose or non-esterifled fatty acid did not reflect energy deficit or surplus. The animals remained clinically healthy during the underfeeding and recovery periods. The results suggest that debility occurring under field conditions in association with reduced food supply may be due to a multiplicity of factors or to severe imbalance of specific nutrients, rather than to energy or protein deficit alone.
There was a difference in efficiency of utilization of energy of 19% between cows in the most severely underfed groups which maintained lactation and those which were not able to maintain lactation. There was evidence that this difference in efficiency was detectable within a few weeks of the start of the period of reduced nutrition. Animals which were less affected in the early stages of food deprivation were also those which maintained the advantage through the deprivation and recovery periods.