FACTORS AFFECTING MILK YIELD AND QUALITY IN COMMERCIAL DAIRY FARMS

Abstract

The research question of this paper was to examine the multifactorial determinants of milk yield and quality in Holstein Friesian dairy cattle with special reference to the impacts of heat stress measured by the temperature-humidity index through a twelve-month study of three hundred lactating cows in three different agroecological areas. Longitudinal data was collected, comprising daily adjustment of milk yield, fortnightly analysis of milk composition (fat, protein, lactose, and somatic cell count), monthly analysis of blood biomarkers, and continuous climatic data. The findings showed that the milk yield decreased gradually from a high of 34.43 kilograms per day in thermoneutral conditions to a low of 19.07 kilograms per day in conditions of extreme heat stress, which is a 44.6 percent decrease, and parity occurred between three cows with the steepest rate of decrease. The percentages of milk fat and protein declined by 13.3 percent and 13.3 percent, respectively, during severe thermal loading, and the levels of lactose had diurnal variation, with afternoon milking being worst hit with a decline in the levels of over 7 percent under extreme conditions. The number of somatic cells increased more than 2 times in the summer months between 145,300 and 367,800 cells per milliliter with heat stress and high stocking density and exhibited synergistic effects on the health of the udder. Analysis of biomarkers showed that cortisol levels almost quintupled, starting at 12.34 to 56.78 nanograms per milliliter, and that the levels of heat shock protein seventy rose by five times, starting at 145.6 up to 789.2 picograms per milliliter as the temperature-humidity index went above eighty and under sixty-eight, respectively. The fatty acid analysis revealed that short-chain fatty acids such as butyric and caproic acid were decreased by 12 and 18 percent, respectively, and stearic acid was increased paradoxically by 10.24 percent during thermal stress, indicating a change in lipid metabolism and mammary synthetic pathways. Economic analysis estimated total losses of 1159.69 United States dollars per cow on farms with more than one hundred and twenty annual heat stress days, comprising 37.89 percent of gross revenue, with the decrease in milk yield taking up 68 percent of the losses. The use of combined mitigation approaches resulted in yield recovery of 98.2 percent in 4.5 days, whereas evaporative cooling only offered the best compromise between cost-efficiency and production recovery. These results can be used to define critical temperature-humidity index values to intervene and give quantitative data on the need to develop integrated management plans that integrate genetic selection of thermotolerance, investments in infrastructure for cooling systems, and strategic nutritional adaptations to maintain dairy production and profitability in rising global temperatures.