[ relationship between growth hormone polymorphism and growth hormone receptor genes with milk yield and reproductive performance in Holstein dairy cows]

The aim of this study was to investigate the potential association between growth hormone GH/AluI and growth hormone receptor GHR/AluI polymorphisms with milk yield and reproductive performances in Holstein dairy cows in Iran. Blood samples of 150 Holstein cows were collected and their genomic DNA was extracted using Gene-Fanavaran DNA extracting kit. Fragments of the 428 bp of exon 5 growth hormone [GH] gene and the 342 bp of exon 10 growth hormone receptor [GHR] gene were amplified using the polymerase chain reaction [PCR] method. PCR products were digested by the AluI restriction enzyme and electrophoresed on 3% agarose gel. Continuous and categorical data were analyzed using linear mixed models through Proc MIXED and logistic regression models through Proc GENMOD of SAS software, respectively. The results showed no relationship between the examined traits and GH/AluI or GHR/AluI genes. A significant relationship was found between GH/AluI polymorphism and dystocia, but the presence of the GH-L allele reduced the incidence of dystocia. The results suggest that the GH-LL genotype reduces dystocia probably by affecting the release of growth hormone; nevertheless, further studies will be needed to examine the relationship between dystocia and GH genotypes.

[ effect of oregano and thyme based essential oils and [beta]-glucanase on performance and nutrients digestibility in broiler chicks fed barley-based diets]

Essential oils [EO] are antimicrobial compounds, but may be beneficial under unfavorable nutritional and environmental conditions. Essential oils produced in Iran are of comparable quality to imported ones. The aim of this study was to compare the effects of Orego-Stim [Essential oil based on Oregano; 0.5 g/kg; imported] and Anti-Biophin [Essential oil based on Thyme; 1 g/kg; local] essential oils on performance and precaecal digestibility of nutrients in broiler chicks fed barley-corn based diets with and without b-glucanase [0.05 g/kg]. At the beginning of the second week of rearing period, 192 chicks of mixed sex were allotted into six groups of four replicates with eight chicks per replicate according to a 2x3 factorial experiment arranged as a completely randomized design. Inclusion of Orego-Stim or Anti-Biophin in barley based diets caused a significant [p<0.05] improvement in total feed conversion, final body weight and nutrients digestibility, without a significant effect of [beta]-glucanase addition to the diets. The type of essential oils [imported vs. local] did not affect the measured characteristics. Feeding broiler chicks with barley based diets, supplemented with essential oils, decreased the anti-nutritional effects of barley grains in these diets and improved broiler performance, without the need to supplement the barley-based diets with b-glucanase. Because of the lack of any significant difference between the imported and locally-produced essential oils, and the higher cost and scarcity of the imported EO, domestic products such as Anti-Biophin at recommended levels can replace the imported ones

Genetic correlation of average somatic cell score at different stages of lactation with milk yield and composition in Holstein cows

Genetic and non-genetic correlations of the average somatic cell score [SCS] at different stages of lactation [100, 150, 200, 305 and 365 days in milk] with lactation performance were estimated based on the first lactation records of Iranian Holstein calving during 2000 to 2009. [Co] variance components were estimated using derivative-free REML based on multiple traits animal models. The estimated genetic correlations between average of first 100 days in milk SCS [SCS[100]] and milk100, fat100, milk305, fat305 and protein305 were 0.14, 0.19, 0.11, 0.15 and 0.17, respectively. The corresponding environmental correlations were -0.13, -0.03, -0.18, -0.10 and -0.13, respectively. The estimated genetic correlations of the average SCS during the first 150 days in milk [SCS[150]] with milk[100], fat[100], milk[305], fat[305] and protein[305] were 0.14, 0.19, 0.11, 0.15 and 0.17, respectively. The corresponding environmental correlations were -0.13, -0.03, -0.18, -0.10 and -0.13, respectively. The estimated genetic correlations of the average SCS during 305 days in milk with milk, fat and protein yield, and fat and protein percentages were 0.12, 0.11, 0.18, -0.05 and -0.08, respectively. The estimated genetic correlation between SCS[100] or SCS[150] with average SCS over longer stages of lactations [SCS[305] and SCS[365]] was 0.99 +/- 0.01. These results indicate that recording SCS data over shorter period of lactation is an alternative approach to reduce the costs of SCS data collection and therefore to expand the SCS recording in the country by increasing both the number of herds and cows involved

[Association between the lactation curve shape and calving interval in Holstein dairy cows of Iran]

This study was carried out to investigate the relationship between early lactation curve parameters and calving interval in Holstein cows of Iran. In order to describe the lactation curve, the incomplete gamma function was fitted to 5,754,428 test-day milk records corresponding to 766,108 lactations on 315,634 cows in 2,448 herds. Cows with higher milk yield during early lactation had shorter calving intervals; however, longer calving intervals increased the 305-d milk production [P<0.01]. Cows with higher yield at the beginning of lactation, steeper ascending, and steeper descending slope had shorter calving intervals [P<0.01]. Calving interval was increased by 2.73 [+/- 0.12] d for every extra kg of milk at peak lactation [P<0.01]. The calving interval was directly impacted by the persistency of milk yield, but milk yield persistency was reduced in cows with shorter calving intervals [P<0.01]