Effects of crossing and environmental factors on production and some constituents of milk in Ossimi and Saidi sheep and their crosses with Chios

Abstract

Milk production and milk constituents were studied in 95 ewes of two purebred groups, Ossimi (O) and Saidi (S), and two F1 crosses with Chios (C) (CO and CS) from September 1991 to April 1993 at the Experimental Animal Farm, Faculty of Agriculture, Minia University, Egypt. Breed of ewe had an effect ( P < 0.01) on total and average daily milk yield and length of lactation. CO ewes had the highest average daily milk yield (574 g), followed by CS ewes (554 g), while O ewes had the lowest (459 g). CS ewes had the highest lactation (86.2 kg in 149 days), followed by CO ewes (85.4 kg in 146 days); S ewes produced 64.7 kg in 135 days, and O ewes produced 55.7 kg in 119 days. Ewes rearing twins produced more milk than those suckling singles, but the differences were not significant. The effect of age of ewe within breed was non-significant on total and average daily milk yield, although ewes aged 3–4 years showed relatively higher milk yields than younger or older ewes. The effect of year of lambing was not significant on daily milk yield, but was significant on both total milk yield and length of lactation. Milk fat (F), total solids (TS) and total solids not fat (SNF) were not significantly influenced by breed, type of rearing, year of lambing or age of ewe/breed. Fat percentage averaged 5.54, 5.82, 5.82 and 5.89 for O, S, CS and CO ewes, respectively. TS ranged between 17.66 and 18.16%, and SNF between 11.95 and 12.34%. For O, S, CO and CS, milk yield reached its peak at 3, 5, 7 and 5 weeks postpartum, respectively, with a corresponding daily milk yield of 615, 609, 832 and 803 g, respectively. Lactation period lasted for 21, 25, 27 and 27 weeks, respectively. Curves for F, TS and SNF percentages indicated a decline during the first 2–3 weeks of lactation, followed by an increase. F, TS and SNF showed a similar pattern in the four breeds, reaching a peak at the end of the lactation period. The figures ranged from 4.2 to 10.4%, from 15.4 to 23.6% and from 11.5 to 13.2% for F, TS and SNF, respectively. Significant and negative linear and quadratic regressions were fitted for daily milk yield on week of lactation; these were (for 2 weeks): O, −49.1 g and −5.2 g; S, −39.9 g and −4.6 g; CO, −50.8 g and −4.6 g; CS, −49.3 g and −3.8 g. Linear regression coefficients of milk constituents on week of lactation were all positive and significant, while the corresponding quadratic regressions were negligible.