The objective of the current study was to estimate the genetic parameters for ewe productivity traits of Harnali sheep by examining non-genetic effects. The data records of 440 animals born to 85 sires and 259 dams were collected with respect to various traits such as litter size at birth (LSB), litter weight at birth (LWB), litter size at weaning (LSW), litter weight at weaning (LWW) and age at first lambing (AFL) for the period of 2001 to 2020. Genetic parameters were estimated by fitting a series of animal models using an average information restricted maximum likelihood (REML) algorithm in WOMBAT software. Least-squares analysis revealed significant (P < 0.05) influences of period of lambing, age and weight of ewe at lambing on the studied traits. These results indicated that heavier ewes had significantly higher (P < 0.05) values of litter weight traits than their counterparts. On the basis of likelihood ratio test, the estimates of direct heritability under best model for AFL, LSB, LWB, LSW and LWW were 0.06, 0.18, 0.09, 0.07 and 0.16, respectively. Maternal permanent environment effect made a significant contribution to the LSB trait (0.20). The genetic correlation between litter size and LWW was negative, while the remaining correlations were positive. The present results suggest that selection based on ewe productivity traits will result in low genetic progress and therefore the management role is more important for better gains.

An experiment was carried out in Egypt using Giza White rabbits to investigate their lactational performance and to estimate the repeatabilities of milk yield and other litter traits. Data on 325 litters from 115 does fathered by 40 sires were used. Lactation traits involved milk yields during the first 7 days, 21 days and 35 days. Litter traits included litter size and weight at birth, number born alive, litter weight and gain at 21 days, litter size and weight at weaning and pre-weaning litter gain. Linear mixed models were used for analysing such data.

Phenotypic variation in milk yield was relatively high during the first 7 days, and decreased thereafter with advance of lactation stage. Year-season effects were significant for most litter traits, while month of kindling affected litter weight and gain at 21 days and milk yield during the first 7 days (P < 0·05 or P < 0·001). Litters kindled during winter had the highest milk yield compared with litters kindled in the other seasons. Milk production, litter size and weight and litter gain had curvilinear relationship with parity (P < 0·05 or P < 0·001). Sire of doe had no significant effects on litter traits studied. Repeatabilities of all traits were low and ranged from 0·001 to 0·134. Litter size and weight at birth were residually correlated with milk yield. Litter weight and gain at 21 days were significantly correlated with the lactational performance of the doe (P < 0·001).

A study of the determinants of inter- and intra-litter variation in muscle fibre number was carried out on five litters of Large White piglets. Fresh frozen, whole mid-belly sections of m. semitendinosus were stained to demonstrate acid-stable myosin adenosine triphosphatase activity. From these sections it was possible to identify which fibres had developed as primary and which as secondary fibres. Estimations of total muscle fibre number, total primary fibre number and ratio of secondary fibres to primary fibres were made for each animal. Results demonstrated that primary fibre number varied between litters (P<0·01) and was responsible for the variation in total muscle fibre number (P < 005) between litters since there was no significant variation in secondary: primary ratio. Within-litter differences in total fibre number could be attributed to both the secondary: primary ratio and primary fibre number, in almost equal contributions. However, when only the largest and smallest extremes of the litters were compared, variation in fibre number was due to the significant difference in the secondary: primary ratio (P<0·01). Taken as a whole, the results appear to show that primary fibre number is responsible for all the variation in muscle fibre number between litters, and also makes a significant contribution, with secondary: primary fibre ratio, to the variation present within a litter. The factors responsible for variations in primary and secondary fibre numbers are discussed.

A total of 1754 records for litter traits of 458 D'man ewes sired by more than 45 rams were analysed to estimate repeatability, heritability and genetic and phenotypic correlations. Repeatability estimated by the intraclass correlation method was 0·11, 0·11, 0·12 and 0·15 for litter sizes at birth and at weaning and litter weights at birth and at weaning, respectively. Paternal half-sib estimates of heritability were 0·09 (s.e. 0·06), 0·04 (s.e. 0·05), 0·15 (s.e. 0·07) and 0·08 (s.e. 0·05), respectively. Genetic correlations among the traits were all positive and varied from 0·17 to 0·72, whereas phenotypic correlations ranged from 0·68 to 0·86.