Compositional quality of milk and its seasonal variation in Jersey cows of Zimbabwe
Keywords:Jersey cows, Season, Protein, Fat, Lactose, Total solid, Solid not fat, Milk urea nitrogen
The compositional quality of milk is the outcome of the synergy of various biological processes within the cow and its external environment. The objective of this study was to investigate the effect of season on the compositional quality of milk in Jersey cows of Zimbabwe. The study material consisted of 813 records of a total of 60 head of Jersey cows collected from a commercial dairy farm in Matabeleland South province in Zimbabwe. For the analysis three seasons were defined: 1-Warm Wet (December-March), 2-Dry Cool (April-August), and 3- dry hot (August-November). Chemical compositions (fat, protein, lactose, SNF, salt) as well as the freezing point, density of collected milk samples were carried out by using the Milk Analyzer (Lactoscan, UK). Statistical data processing was carried out by applying the General Linear Model procedure, SAS system (1999). Duncan multiple range test was used to compare the means within a group, difference was considered as significant if (P0.05) and the results were presented as Mean±SE. The mean fat percent were 4.94±0.05, 4.62±0.08, and 4.56±0.05, and mean protein percent were 3.72±0.02, 3.50±0.03, and 3.49±0.03 for warm wet season(December-March) dry cool season (April-August), and dry hot (August=November), respectively. The warm wet season had maximum milk urea nitrogen (17.24 ±0.54mg/dl) while the dry cool season (April-August) had the minimum milk urea concentration of 12.38±0.82. The results showed that milk collected in the warm wet season (December-March) had significantly higher fat and protein as compared to dry cool season(April-August) and dry hot (August=November). However, no seasonal variation was evident in total milk solids (TS; %), solids non-fat (SNF, %), and milk density. Moreover, lactose (4.74%) contents were high in the dry hot season (August-November), while maximum milk urea nitrogen content (17.24%) was observed in the wet warm season. The mean concentration of milk urea nitrogen in the study of 14.84±4.60 mg/dl indicates a good balance of energy and protein in the diet. Fat, protein, lactose, and milk urea nitrogen contents of milk significantly varied with the season. Synchronous changes in protein and fat percent in raw milk were much more distinct as the season progresses through the wet and dry season.
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