EFFECTS OF LOW FLUCTUATING TEMPERATURES ON FARM ANIMALS: IV. INFLUENCE OF TEMPERATURE ON MILK YIELD AND MILK COMPOSITION

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Abstract
Changes in milk yield and milk composition from mature Holstein-Friesian cows managed under low fluctuating environmental temperatures have been presented. The experiment conducted at the University of Saskatchewan, Saskatoon, lasted for 106 days during the winter of 1956–57. Loafing barn temperatures, measured continuously in degree-hours per day (d-h/day) ranged from 110 to 1202 and daily minimum ambient air temperature (DMAAT) varied from −5° to 38°F.As temperature decreased below 25°F., daily yield of milk decreased significantly. Milk yield was unaffected by d-h/day at mean temperatures over 25°F. (600 d-h/day) and on days colder than 600 d-h/day the temperature effect on milk yield was curvilinear. The rate of decline in milk yield (pounds) was four times greater on days when DMAAT was below 10°F. than on days when DMAAT was above 10°F. While DMAAT had a significant effect on milk total-solids percentage and a highly significant negative effect on crude protein yield, the effect of d-h/day on these two factors was not significant. Neither DMAAT nor d-h/day had a significant effect on butterfat yield and percentage, fat-corrected milk yield, total-solids yield, solids-not-fat yield and percentage, or crude protein percentage.Stage of lactation had a significant effect on all characteristics studied except butterfat percentage.Under conditions of declining lactation and a high, variable plane of nutrition, cows that had been subjected to gradually cooling variable low temperatures were influenced by low daily minimum temperatures (DMAAT) to a greater degree than low mean daily temperatures (d-h/day).