Genetic analyses of scrotal circumference size and growth in Rambouillet lambs

Polymorphism in IGFALS gene and its association with scrotal circumference in Hu lambs

Scrotal circumference is an important reproductive index of breeding rams, which has a high genetic correlation with ejaculation volume and semen quality. In this study, the scrotal circumference of 1353 male Hu sheep at different stages of development was measured and descriptive statistical analysis was performed. The results showed that the coefficient of variation of scrotal circumference at each stage was greater than 10%, and its heritability were moderately to high, ranging from 0.318 to 0.719. We used PCR amplification and Sanger sequencing to scan the polymorphisms of the IGFALS gene, and performed association analysis with the circumference of the scrotum at different stages. We identified a synonymous mutation g.918 G > C in exon 1 of the IGFALS gene, and this mutation was significantly associated with scrotal circumference at 100, 120, 140, 160 and 180 days (p < 0.05). Therefore, IGFALS gene polymorphism can be used as a molecular marker affecting scrotal circumference of Hu sheep, which can provide a reference for future molecular marker-assisted selection of scrotal circumference in sheep.

Detection of chromosomal segments underlying scrotal circumference in ram lambs and age at onset of puberty in ewe lambs

Scrotal circumference (SC) is highly correlated with total sperm production and quality of the produced semen. In ewe lambs, puberty is an important reproductive trait and extreme delay in reaching puberty will have a negative effect on breeding efficiency. To identify genomic regions (QTL) underlying variation in SC and age at onset of puberty in ewe lambs (AP), a whole genome scan was performed with 169 microsatellites covering the ovine autosomes. Progeny (360 animals) from six half-sib families in a population of Kermani sheep, an indigenous fat tailed sheep breed in south-east of Iran, were recorded for SC and AP. Linkage analysis using the interval mapping approach indicated a total of 21 QTL for the studied traits on nine chromosomes (OAR1, 2, 3, 5, 6, 9, 11, 18 and 24), including a 5% genome wide significant QTL for SC on OAR5. There was evidence for the overlap of QTL affecting SC and AP on OAR5 and OAR9. The size of the QTL effect ranged from 0.8 to 1.6 in units of the phenotypic standard deviation. Although QTL for testis size in ram lambs have been mapped, this is the first report of QTL for age at onset of puberty in ewe lambs. Pursuing the underlying causes of these QTL may shed light on the molecular aspects of male and female reproductive development in sheep.

Developmental changes in testicular interstitium in the Najdi Ram Lambs

This experiment was designed to study the relationship between growth rate and sexual development in Najdi ram lambs. Forty-five Najdi ram lambs were used in nine age groups (1-9th month age), keeping 5 lambs in each group. Results show that mean testis size and scrotal circumference increased at a constant rate, reaching a maximum value of 392.00 ± 2.00 g and 25.00 ± 0.32 cm respectively, at the age of 9 months. A similar trend of growth was observed for the mean body weight, reaching a maximum value of 40.2 ± 0.20 kg at the age of 9 months. There was a positive correlation between the increasing rates of body weight and size of the testis. There were significant differences (P < 0.05) in testis size, scrotal circumference and body weight of lambs between all ages (1-9 months). The histological section of testis showed that a small number of mature sperms appeared in the eighth month of age and their numbers increased in the ninth month. In conclusion, the current findings indicated that puberty in Najdi rams occurs between the 8th and 9th months of age.

Heritabilities and genetic correlations of body weight, testis growth and ewe lamb reproductive traits in crossbred sheep

Heritabilities (h2) and genetic correlations (rc) involving body weights, measures of testes size and ewe lamb reproduction were calculated using 953 spring-born lambs produced during formation of a three-breed composite population containing 0·50 Dorset, 0·25 Rambouillet and 0·25 Finnish Landrace breeding. The h2 of body weight ranged from 0·2 to 0·3 between 45 and 150 days of age, but increased to 0·41 at the start of breeding of ewe lambs at about 6 months of age. Additive maternal effects were not important, perhaps because intensive housing encouraged cross-suckling. Testes size was measured as scrotal circumference (SC), SC with linear adjustment for weight (SCW) and SC divided by the one-third power of body weight (RSC). The h2 of SC traits was highest at 90 days (0·52 for SC, 0·62 for RSC and 0·57 for SCW), and h2 for age at maximum SC growth rate (i.e. TI, the inflexion point of a logistic SC growth curve) was 0·49. The h2 of ewe lamb fertility in autumn was 0·09 but the h2 for frequency of remating the following spring was 0·41. The h2 for ewe lamb litter size in these data was zero. At 90 days, rc between alternative measures of testes size exceeded 0·86; rG with body weight were 0·67 for SC, 0·53 for RSC and –0·74 for TI. The rG with ewe lamb fertility for 90-day weight, SC, RSC and SCW and for TI were –0·25, 0·20, 0·25, 0·38 and –0·32, respectively. The rc for these traits with spring remating were 0·34, 0·34, 0·26, 0·10 and –0·48, respectively.

Evaluation of mathematical models to describe testicular growth in Blackbelly ram lambs

The primary objective was to compare various mathematical models to describe scrotal circumference (SC) and paired testis volume development in Blackbelly ram lambs. The study was conducted in the state of Querétaro, México (20° 43' N, 100° 15' W). Spring-born Blackbelly ram lambs (n = 41) were housed outdoors and fed alfalfa hay and concentrate. Body weight, SC, and testis length, diameter, and volume were recorded every 2 wk from 24 to 172 d of age (June 18 to November 3). The following mathematical functions were used to model SC-age and testis volume-age relationship: Von Bertalanffy, Brody, Gompertz, Logistic, and Richards. The suitability of the models was evaluated based on parameter values and standard errors, residual mean square, the coefficient of determination (R(2)), and the average prediction error (APE). All models, except for Brody's, had good fit to SC (R(2) > 0.98) and testis volume (R(2) > 0.95), and produced similar growth curves in the range of ages studied. The logistic model predicted SC at maturity quite well, 33.6 ± 0.6 cm as compared with 33.9 ± 0.5 cm observed in adult animals; all models had APE's smaller than ± 7% between 56 and 168 d of age. The Bertalanffy model predicted testis volume at maturity quite well, 513 ± 22 cm(3) as compared with 488 ± 20 cm(3) calculated for adult animals. The logistic model had a good fit to testis volume during the period of study, but underestimated the volume at maturity by 28%. All models, except for Brody's, had APE's smaller than ± 14% between 98 and 168 d of age. The logistic and Bertalanffy models predicted the inflection point for SC at 83 and 59 d of age, and testis volume at 116 and 109 d of age, respectively. In conclusion, all models, except for Brody's, had good fit to actual SC and testis volume data in the range of age evaluated, whereas the logistic and Bertalanffy's models made the best predictions for adult SC and testis volume, respectively.

Selection for easier managed sheep

Current alterations in the farm environment, such as a reduced number of farm workers, may mean that sheep genotypes that are highly dependent on man for nutritional and reproductive success will experience poorer welfare within that environment. In the past 30 years, average flock size has doubled, and flocks of over 1,000 ewes managed by one stockperson are common. The reduction in the ratio of stockpeople to sheep affects animal welfare, with less time for tasks such as healthcare and inspection. It has also led to increased interest in the development of new genotypes that are better able to look after themselves. Selection and management of sheep to promote behaviours associated with survival, and selection of robust animals that require less human intervention for good welfare, are important breeding goals. As these animals will receive less inspection at close quarters, selection for resistance to disease will have significant animal welfare benefits. In addition, the development of sheep lines that require little or no intervention at lambing will be important. In areas where wool is not valuable, the use of wool-shedding breeds to avoid the stress associated with shearing, and to reduce the incidence of flystrike are already proving to be beneficial. Importantly, this selection should not be interpreted as providing no care to these animals, and careful management during the production of these genotypes is needed to avoid at least transient welfare problems where genotypes and environment (eg lower shepherding) are mismatched.

Evolução do peso testicular de cordeiros da raça Santa Inês alimentados com diferentes níveis de energia

Avaliou-se a evolução do peso testicular de cordeiros Santa Inês, alimentados com diferentes níveis de energia. Foram utilizados 64 cordeiros, distribuídos em quatro tratamentos: A - 8,7%; B - 17,3%; C - 26,0% e D - 34,7% de fibra em detergente neutro (FDN), proveniente da forragem na dieta, determinando a variação no consumo de energia metabolizável. Quatro animais de cada tratamento foram abatidos nas idades pré-determinadas de 43, 83, 123 e 173 dias de idade. Os testículos foram separados dos respectivos epidídimos e pesados separadamente. Os animais que receberam as dietas A e B foram os que apresentaram maior consumo de energia metabolizável (14,11Mcal/PV0,75), os mais pesados (18,89kg e 17,09kg, respectivamente) e os de maiores pesos dos testiculos (62,54g e 27,16g, respectivamente), indicando que o desenvolvimento testicular é altamente dependente do desenvolvimento corporal e da quantidade de energia metabolizável consumida. A predição do peso dos testículos por meio da circunferência escrotal mostrou ser mais eficiente do que por meio da idade e do peso vivo dos animais.

Reproductive characteristics of Ethiopian highland sheep. I. Genetic parameters of testicular measurements in ram lambs and relationship with age at puberty in ewe lambs

A study was conducted to estimate heritabilities of, and genetic correlations among, body weight (WT) and testicular measurements - scrotal circumference (SC), testicular diameter (TD), testicular length (TL) and epididymal diameter (ED) - in ram lambs between 6, 9 and 12 months old, and relationship of the testicular traits with age at puberty in ewe lambs (AP). Two fat-tailed sheep breeds, the Horro and Menz, indigenous to the Ethiopian highlands were studied. Experimental lambs were produced by mating 250 oestrus-synchronized ewes of each breed to 10 sires in a single-sire mating system over three mating periods which produced, for this study, a total of 361 ram lambs and 148 ewe lambs, with substantial pedigree information, in two dry seasons (October/November 1992 and 1993) and one wet season (June/July 1993). Mean AP was 322.7 days. Breed was not significant (P0.05) for all testicular measurements, except ED at 9 months for which the Horro had a higher (P<0.01) value (20.6, s.e. 0.38 versus 19.3 s.e. 0.30). Horro ewe lambs had their first oestrus 28 days earlier (P<0.05) than the Menz. Heritability estimates were obtained from a sire model (M1) and from an individual animal model with additive direct and maternal effects (M2). The maternal effect was not fitted in M2 for AP. Repeatability and heritability estimates were also obtained by analysing records at the three ages in a repeated measures model (M3). M1 and M2 heritability estimates were generally low to moderate but were associated with large standard errors. Heritability estimates for testicular measurements were generally similar to those for WT. Among the testicular measurements, SC had the highest heritability estimates at 6 (0.45, s.e. 0.24 for M1) and at 12 months (0.41, s.e. 0.21 and 0.41, s.e. 0.20 for M1 and M2, respectively). Model 3 heritability estimates were 0.29 (s.e. 0.14), 0.24 (s.e. 0.12), 0.09 (s.e. 0.07), 0.11 (s.e. 0.08) and 0.12 (s.e. 0.08) for WT, SC, TD, TL and ED, respectively. Only repeatability estimates for WT (0.34, s.e. 0.02) and SC (0.25, s.e. 0.03) were significant. Heritability of AP was estimated at 0.16 (s.e. 0.21) by M1 and 0.14 (s.e. 0.19) by M2. Genetic correlations of AP with testicular measurements, especially with SC (-0.57, s.e. 0.38 and -0.78, s.e. 0.33, at 9 and 12 months, respectively) and TD (-0.72, s.e. 0.33 and -0.83, s.e. 0.48), were desirable and generally high. Adjustment of testicular measurements for liveweight consistently resulted in a reduction in estimates of heritability and genetic correlations. SC was suggested as the most appropriate selection candidate for the genetic improvement of both male and female reproductive performance in these breeds.