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The first lactation production records of 351 Sahiwal cows maintained at National Dairy Research Institute, Karnal over a period of 52 years (1961-2012) were used to estimate the persistency measures using different methods viz. Rao and Sundaresan method, 1982 (P₁), P_TOMAX2 (P₂), P_TOMAX3 (P₃), P_SD2 (P₄), P_SD3 (P₅), P_YV (P₆) and Wood's function (P₇). The average persistency of milk yield estimated by above different methods viz. was 194±1.10, 145.10±0.81, 156.71±1.01, 2.29±0.04, 2.20±0.03, 1.00±0.03 and 0.14±0.02, respectively. The T_OMAX2 method was found to be most efficient out of all ratio methods and P_SD3 method was observed to be most efficient amongst variation of yields method. However, mathematical lactation curve model was found to be least efficient as compared to other methods for estimation of persistency.

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The study was undertaken to determine the composition of colostrum and milk of Hill cattle during postpartum period and compared them to Sahiwal and crossbred cow. Fifteen colostrum samples per day from each group of cow (as per availability) were collected during first five postpartum days while as milk samples were collected from eight cow each of Sahiwal and crossbreds and six form Hill cow, at fortnightly interval up to 32 weeks postpartum. These samples were subjected to various physico-chemical analyses. There was a significant (P?0.05) difference between overall mean protein per cent, pH and electrical conductivity in the colostrum of Hill cow, Sahiwal and crossbred cow but lactose per cent did not diffe significantly. In milk there was a significant (P?0.05) difference between overall mean of fat, protein, solid not fat, total solids per cent, pH, electric conductivity, somatic cell count and milk yield of Hill cow, Sahiwal and crossbreds while non-significant (P?0.05) difference was noticed for lactose per cent and specific gravity. The colostrum of Hill cow and Sahiwal were richer in protein, fat, lactose, TS and ash content as compared to crossbred cow. Milk of Hill cow had higher content of protein, fat, SNF, TS and lower pH, EC and SCC compared to crossbreds and Sahiwal.

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