Response surface and fixed effects models of non - genetic factors for dairy cows in Saudi Arabia

ABSTRACT

Response surface model of statistical analysis was used to quantify the relationship between non-genetic factors [NGF] such as days open [DO], days in milk [DIM], age at calving and milk production. Data included 103.776 records; each one had cow identification, non genetic traits and production traits such as total milk production. 305-milk yield and peak yield. Least square means of three farms were 10467, 11047 and 10697 liters of milk respectively. Cows calved on fall-winter season produced 10839 liters, compared with 10636 liters for cows calved in spring-summer season. Second lactation cows gave the highest production [11, 105 liters], and sixth lactation cows produced the lowest production [10, 283 liters]. Significant parameters [p < .01] supported the linear and quadratic relationship between age at calving and total yield, 305-dyield and peak milk production, respectively. The DIM had a significant linear effect on milk production [p < .01]. Also, quadratic representation of DIM was observed along the whole milk curve. Days open showed no linear significant effect on milk production. However, significant quadratic effect [p < .05] was found between DO and 305-d yield, The ANOVA of fixed model showed a significant effect of NGF on production traits