Physiological and production responses to feeding schedule in lactating dairy cows exposed to short-term, moderate heat stress.

The objective of this research was to characterize the production responses of lactating dairy cows during and after short-term, moderate heat exposure, and to determine whether evening (p.m.) feeding would alleviate the associated production losses. In a two-period, cross-over design, eight mature lactating cows were fed a total mixed ration at either 0830 or 2030 h. Each 15-d period consisted of a 5-d thermoneutral phase, a 5-d heat stress phase and a 5-d thermoneutral recovery phase. Mean daily vaginal temperature and respiration rate increased by 0.6 +/- 0.04 degrees C and 27 +/- 1.3 breaths/min, respectively, during short-term heat exposure. Daily dry matter intake, milk yield and solids-not-fat were depressed by 1.4 +/- 0.13 kg, 1.7 +/- 0.32 kg and 0.07 +/- 0.023%, respectively, during heat exposure. During the recovery phase, dry matter intake remained depressed, milk protein declined by 0.05 +/- 0.020%, and daily milk yield exhibited a further decline of 1.2 +/- 0.32 kg. Time of feeding had no effect on vaginal temperature, respiration rate, dry matter intake, water intake, milk yield, fat-corrected milk, protein percent, solids-non-fat percent or somatic cell count during heat exposure or during the recovery period that followed. Fat percent was, however, significantly lower in p.m.-fed animals. These data indicate that short-term, moderate heat stress, which occurs during the spring and summer months in Canada and the Northern United States, will significantly decrease production in the lactating cow. Shifting from morning to evening feeding did not alleviate production losses associated with this type of heat stress.

Influence of moist heat treatment on ruminal and intestinal disappearance of amino acids from canola meal.

Three mature Angus steers fitted with large ruminal cannulas and three Holstein steers each fitted with T-shaped cannulas in the proximal duodenum and reentrant cannulas in the terminal ileum were used to study the effect of moist heat treatment on AA digestion of canola meal in each segment of the digestive tract. Canola meal was treated with moist heat at 127 degrees C for 15 or 45 min. Degradation of AA in the rumen was estimated using small nylon bags incubated for .1, 8, 16, and 24 h in the rumen. Digestion of AA in the small and large intestines and total tract were estimated using separate sets of bags in a sequence of ruminal in situ incubation, in vitro incubation in an acid-pepsin solution, and a mobile bag technique. Heat treatment for 15 or 45 min reduced concentrations of Lys by 15.9 and 29.2% and Arg by 8.0 and 15.2%, respectively. Heat treatment for 15 or 45 min significantly reduced the degradation of AA in the rumen; the availability of AA in the small intestine increased in proportion to the decreased ruminal degradation. Digestion of AA in the large intestine was 5 percentage points higher after heat treatment for 45 min than with no heat treatment. Apparent digestion of AA in the total tract was unaffected by 15 min of heating; however, 45 min of heating reduced digestion.(ABSTRACT TRUNCATED AT 250 WORDS)