Improving feed efficiency of dairy cows has a significant effect on economic profitability due to the reduction of feed costs. To eva‎luate the economic impact of improving feed efficiency on breeding objectives for Iranian Holsteins, economic weights were calculated using trait-by-trait or multi-trait bio-economic model. Meta-analysis was conducted to analyze the genetic relationships between feed efficiency and other traits (productive, reproductive, productive life, type and body size traits). Weighted mean heritabilities estimated for residual feed intake, dry matter intake, milk yield, fat yield, protein yield, productive life and days open 0.19, 0.21, 0.22, 0.22, 0.22, 0.10 and 0.03, respectively. The genetic correlation of residual feed intake with milk yield was low and positive, but with fat and protein yield, it was low and negative. In addition, the genetic correlation of residual feed intake with days open and productive life was negative. This correlation was moderate for productive life and high for days open. The genetic correlation of dry matter intake with milk, fat and protein yield as well as productive life was positive and high, but with days open was negative and low. Average economic coefficients per cow per year in all herds were estimated to be IRR 14280 per kg of milk yield; IRR 291060 per kg of fat yield; IRR 232260 per kg of protein yield; IRR - 790860 daily residual feed intake; IRR - 613200 total daily dry matter intake; IRR 702588 per month of longevity and IRR- 113820 per day of days open. Iranian selection index was revised to improve feed efficiency based on the theory of selection index through a deterministic model. An investigation of different selection indices that included direct and indirect selection for feed efficiency traits showed that the best total selection index response was observed when RFI was directly included as a selection criterion. The Iranian selection index was revised to improve feed efficiency, and the feed efficiency sub-index (FE$) introduced by the Holstein Association of the United States of America was adopted to reflect Iran’s economic and production systems. However, there were discrepancies between Iranian and US genetic coefficients in the sub-index, which could be attributed to differences in genetic and phenotypic parameters, as well as the economic value of each trait. More accurate estimates of economic values for each trait in FE$ could be obtained by collecting dry matter intake from Iranian herds and conducting genetic eva‎luations for residual feed intake. This study eva‎luates the estimated economic impact of nutritional grouping with stall stocking density in large industrial dairy herds located in Isfahan province using a stochastic Monte Carlo simulation model developed and described in a companion paper. The calculated Difference income over feed costs (IOFC, IRR/cow per yr) between grouping strategies and 1 groupwith K-means clustering algorithm without stall stocking density among the herds ranged from IRR448560 to IRR4333980, with an average of IRR2466744 for 2 groups, IRR2581824 for 3 groups and IRR2627856 for 4 groups. The improved IOFC was explained by increased milk sales and lower feed costs. Higher milk sales were a result of fewer cows having a milk loss associated with low BCS in multi-group scenarios. The percentage of N fed captured in milk increased with more than 1 group, and was the most important factor for improved economic efficiency of the grouping strategies.

علي صادقي سفيدمزگي

غلامرضا قرباني خراجي , پويا زماني , ويكتور كبررا

سعيد انصاري مهياري , محمود وطن خواه , مهدي بهرامي