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1. In current breeding programmes, uniformity of end products and producing animals that are robust to environmental challenges are desirable. Several studies have provided evidence of the presence of genetic heterogeneity of residual variance and proposed that it could be possible to increase uniformity of livestock productions by selection. The present study aimed to define the micro environmental sensitivity of dual-purpose chickens for body weight at hatch. 2. The data set consisted of 24,321 female and 21,547 male chickens' records of hatch weight from 19 consecutive generations of Mazandaran fowl. The statistical analysis was carried out in a two-step approach: first, an animal model was fitted to the data and then, the impact of additive genetic effects on the residual variance of the studied trait was investigated. 3. The estimate of heritability for body weight at hatch was in the range of 0.23-0.25 for female and 0.14-0.16 for male offspring, respectively. The proportion of maternal environmental variance to phenotypic variance ranged from 0.24 to 0.27 for female and 0.17 to 0.24 for male offspring. Heritabilities in females were higher than males. Estimates of the heritability of residual variance ranged between 0.067 and 0.090. The genetic coefficients of variation were high ranging between 0.83 and 0.86. Genetic correlations between hatch weight and its residual variance estimates from bivariate analysis were -0.39 and -0.44 in females and males, respectively. 4. The results suggest that there is an opportunity to simultaneously improve body weight and the uniformity of body weight by selecting for lower residual variance in native chickens.

In this study, 65,971 lactations on 41,842 cows in 64 herds were used to determine the association between dry period length (DPL) and lactation performance, lactation curve, calf birth weight, and the incidence of calving difficulty during the subsequent parity in Holstein dairy cows in Iran. The length of the dry period was classified into 7 categories: 0 to 35d, 36 to 50d, 51 to 60d, 61 to 70d, 71 to 85d, 86 to 110d, and 111 to 160d. Cows with the standard DPL (51 to 60d) produced more 305-d milk, fat, and protein over the next lactation compared with those with shorter dry periods. Shorter dry periods (0 to 35d and 36 to 50d) were associated with lower initial milk yield, steeper inclining and declining slopes of the lactation curve, and higher milk persistency compared with dry period length of 51 to 60d. Peak lactation was achieved later in cows with 0- to 35-d and 36- to 50-d dry period length than in those with dry period length of 51 to 60d. We also observed a relationship between DPL and calf birth weight: smaller calf birth weight was recorded with a dry period of 51 to 60d compared with longer dry periods. The incidence of calving difficulty did not differ in cows with 51- to 60-d dry period compared with cows with 0- to 35-d and 36- to 50-d dry periods. In conclusion, the results of this study did not support previous findings that suggested a shorter dry period could be beneficial to dairy production., (Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Survival records from 1,763 Kermani lambs born between 1996 and 2004 from 294 ewes and 81 rams were used to determine genetic and non-genetic factors affecting lamb survival. Traits included were lamb survival across five periods from birth to 7, 14, 56, 70, and 90 days of age. Traits were analyzed under Weibull proportional hazard sire models. Several binary analyses were also conducted using animal models. Statistical models included the fixed class effects of sex of lamb, month and year of birth, a covariate effect of birth weight, and random genetic effects of both sire (in survival analyses) and animal (in binary analyses). The average survival to 90 days of age was 94.8%. Hazard rates ranged from 1.00 (birth to 90 days of age) to 1.73 (birth to 7 days of age) between the two sexes indicating that male lambs were at higher risk of mortality than females (P < 0.01). This study also revealed a curvilinear relationship between lamb survival and lamb birth weight, suggesting that viability and birth weight could be considered simultaneously in the selection programs to obtain optimal birth weight in Kermani lambs. Estimates of heritabilities from survival analyses were medium and ranged from 0.23 to 0.29. In addition, heritability estimates obtained from binary analyses were low and varied from 0.04 to 0.09. The results of this study suggest that progress in survival traits could be possible through managerial strategies and genetic selection.

Calving records of Holstein dairy cows from April 1998 to September 2006 comprising 16 herds with 104,572 calving events representing 4,045 twin births were used to evaluate reported twinning rate, calf sex ratio, stillbirth, and abortion rates in single and twin births. Overall, the reported twinning rate was 3.9%, and twinning increased with parity [1.1% for primiparous cows vs. 5.7% for cows in their fourth or greater lactation; odds ratio (OR) = 5.50]. Regardless of parity, the greatest twinning rate was observed when conception occurred in fall season from September to December (OR = 1.17). Calf stillbirth was greater after twin births, with 18.8% of twin calving events resulting in one or both calves as stillborn, compared with 4.0% for singleton births (OR = 7.58). Calf stillbirth for multiparous cows was 2.9% for single births and 18.0% for twin births (OR = 7.08), whereas for primiparous cows, stillbirth was 6.6% for singletons and 27.7% for twins (OR = 5.85). Calf sex ratios (male, M; female, F) were 52.4% M and 47.6% F for singleton calves and 28.2% MM, 48.9% MF, and 22.9% FF for twin calves. The mean abortion rate was 13.4%, with 13.8% for single births and 4.2% for twin births (OR = 1.22). Abortion rate for multiparous cows was 15.9% for single births and 4.0% for twin births (OR = 4.31), whereas for primiparous cows, abortion rate was 9.4% for single births and 5.4% for twin births (OR = 1.89). Although milk production, as a causative factor associated with twinning, increased in recent years, twinning rate decreased over the years.