Scielo RSS <![CDATA[South African Journal of Animal Science]]> vol. 39 num. 3 lang. en <![CDATA[SciELO Logo]]> <![CDATA[<b>The effect of age at photostimulation of male broiler breeders on testes growth and the attainment of sexual maturity</b>]]> Male broiler breeders were photostimulated at different ages (56, 77, 98, 119, 147 and 161 d) during the period of growth prior to achieving sexual maturity to observe their response to photoperiod stimulation. Birds were sampled at regular intervals to measure the average testis weight - these values responding curvilinearly to the age at photostimulation, similar to the attainment of sexual maturity observed previously in females. However, males reached sexual maturity at an earlier age than females, as measured by the start of semen production. Based on the age at first semen production, no differences in the mean age at sexual maturity (ranging from 164 to 172 d) resulted from the different ages at photostimulation. Testis weights from males on different photostimulation treatments showed that some males respond to early stimulation, but from 189 d of age some of these early photostimulated males still had an average testis weight of less than 10 g, while males photostimulated 98 d and later all had an average testis weight over 10 g. Serum testosterone concentration measured at 351 d also showed that early photostimulation resulted in two groups of birds that either responded or not. At 351 d the serum testosterone concentration was more evenly distributed in males photostimulated after 98 d, while males photostimulated before 98 d had either high or low serum testosterone concentrations. Directional asymmetry was observed in testis weights, with the left testis being bigger than the right. Other bilateral traits measured also showed directional asymmetry, an indication of developmental instability. However, the degree of relative asymmetry was not related to treatment. All males should respond to photostimulation by 98 d but some respond earlier, and these could be used by broiler breeding companies to eliminate seasonality in these birds. <![CDATA[<b>Genetic parameters for subjectively assessed wool and conformation traits in the Tygerhoek Merino flock</b>]]> Records of the Tygerhoek Merino resource flock were used to estimate genetic, phenotypic and environmental parameters for subjectively assessed wool and conformation traits. The database consisted of records of 4 495 animals, the progeny of 449 sires and 1 831 dams born in the period 1989 to 2004. The pedigree records have been collected between 1969 and 2004. Direct heritability estimates (h²a) for subjective wool traits ranged from 0.15 for face cover score to 0.50 for woolly face score. Corresponding h²a for subjective conformation traits ranged from 0.13 for topline (TOPL) to 0.39 for total fold score (TOT). Maternal heritability estimates were all below 10% where applicable. The proportion of the total phenotypic variance due to the maternal permanent environment variance (c²pe) amounted to 5% for general head conformation (GEN). The genetic correlation between animal effects ranged from -0.70 to 0.21 where applicable. Among the subjective wool traits favourable genetic correlations (r g) were estimated between regularity of crimp (ROC) and wool colour (COL) (0.31), for wool quality (QUAL) with ROC (0.49) and COL (0.26) and between staple formation (STAPL) and belly and points (BANDP) (0.58). The relationships between ROC and STAPL (-0.49) and for QUAL with STAPL (-0.45) and BANDP (-0.20) were unfavourable. The noteworthy relationships among subjective conformation traits were those between the conformation of the hind legs and the conformation of the front legs (0.71) and of GEN and TOPL with TOT (-0.31 and -0.47 respectively). The r g of significance between subjective wool and conformation traits were variable in sign and magnitude. These results indicated the possibility to achieve sustained genetic improvement by selection for subjective wool and conformation traits in South African Merino sheep. <![CDATA[<b>Relationships of subjectively assessed wool and conformation traits with objectively measured wool and live weight traits in the Tygerhoek Merino flock</b>]]> Records of the Tygerhoek Merino resource flock were used to estimate genetic, phenotypic and environmental parameters between subjective wool and conformation traits with objective wool and live weight traits. The database contained records of 4 495 animals, the progeny of 449 sires and 1 831 dams, and born from 1989 to 2004. On the genetic level (r g) live weight was favourably related to regularity of crimp (ROC) (0.20), woolly face score (WFS) (0.21), general head conformation (GEN) (0.67), conformation of the hind legs (HOCKS) (0.36), conformation of the front legs (FQ) (0.42), topline (TOPL) (0.25) and total fold score (TOT). Estimates of r g were favourable for clean yield with wool quality (QUAL) (0.30), wool colour (COL) (0.45), wool oil (OIL) (-0.44), staple formation (STAPL), belly and points (BANDP) (0.24), face cover score (FCS) (0.18), GEN (0.25), HOCKS (0.19), TOT (-0.26) and FQ (0.18). Clean fleece weight (CFW) was favourable correlated 'to QUAL (0.18), STAPL (0.39), BANDP (0.48) and GEN (0.23). Staple length was favourably related to COL (0.16), BANDP (0.40) and WFS (0.16) and negatively related to OIL (-0.33). Staple strength was favourable correlated to ROC (0.33) and FQ (0.39). Fibre diameter was favourable correlated with QUAL (-0.32), ROC (-0.28), FCS (-0.32), pastern score (PS) (-0.16) and TOPL (-0.18). Coefficient of variation of fibre diameter (CVFD) was favourably correlated with QUAL (-0.50), ROC (-0.73), HOCKS (-0.17), FQ (-0.33) and TOPL (-0.25). In contrast, unfavourable correlations occurred for SS with TOT (0.25), for FD with STAPL (0.59), BANDP (0.37), HOCKS (0.13) and TOT (0.13). Other unfavourable genetic correlations were between CFW and TOT (0.28) and between CVFD and STAPL (0.49). The results showed that selection for LW and objective wool traits will not seriously compromise subjective wool and conformation traits, barring a few exceptions. <![CDATA[<b>The effect of single or combined dietary supplementation of prebiotics, organic acid and probiotics on performance and slaughter characteristics of broilers</b>]]> A study was conducted to investigate the effect of dietary supplementation of an organic acid, a probiotic or a prebiotic alone or the prebiotic combined with the organic acid or the probiotic on the performance and slaughter characteristics of broiler chickens fed a maize-soya based diet. The six dietary treatments were: a basal diet (negative control) and diets containing 0.5 g mannan oligosaccharide/kg (prebiotic), or 1.0 g formic acid/kg (organic acid), or a probiotic at 0.5 g/kg, or 0.5 g prebiotic/kg + 1.0 g organic acid/kg, or 0.5 g prebiotic/kg + 0.5 g probiotic/kg feed. Each treatment consisted of eight pens with 50 birds per pen (25 male + 25 female). All dietary supplements, alone and in combination improved live weight significantly at both 21 and 42 days of age compared with the control. However, combinations of the prebiotic with either the organic acid or the probiotic had no additive benefit at 21 and 42 days of age in comparison with the prebiotic alone. The feed intake of the birds was significantly increased with prebiotic supplementation at day 21, but not at day 42. Organic acid significantly improved feed conversion ratio at day 21. The combination of prebiotic and probiotic significantly improved the feed conversion ratio at both 21 and 42 days in comparison with the control. At days 21 and 42 bird mortality was significantly higher in the treatments containing organic acid and organic acid with the prebiotic. In the female birds no slaughter traits were affected by dietary treatments. However, liver weight as a percentage of live weight in the male birds was significantly lowered with prebiotic and probiotic supplementation. Prebiotic supplementation with organic acid resulted in a significantly lower weight of the small intestines compared with the control. In general, the different feed additive regimens that include the prebiotic, probiotic, organic acid, prebiotic with organic acid and prebiotic with probiotic improved the growth rate of the birds significantly compared to the control treatment. The significant improvement in feed conversion ratio when the prebiotic and probiotic were supplemented together suggests a synergism between them. <![CDATA[<b>Effect of bleeding method and low voltage electrical stimulation on meat quality of ostriches</b>]]> The effect on ostrich muscle quality of an additional thoracic stick (TS) to the normal ventral throat slit to bleed ostriches after electrical stunning was evaluated. The additional TS had no negative or positive effect on the drip loss, cooking loss, colour or pH and temperature readings of the fillet (Muscularis iliofibularis), big drum (M. gastrocnemius, pars interna) and inside loin (M. iliotibialis cranialis). None the less, personal observations would recommend the use of TS due to ethical considerations. An early post mortem low voltage electrical stimulation (ES) of the carcasses also had no influence on the cooking loss, drip loss and colour of these muscles. Electrical stimulation did result in a lower pH45 in both the fillet and big drum muscles. However, after 24 h the pH of the muscles did not differ. Electrical stimulation also caused elevated initial muscle temperatures, although this effect was only temporary due to the efficient cooling mechanism used in the abattoir. Electrical stimulation also had no effect on the Warner Bratzler shear force values in the fillet. It can be concluded that low voltage ES has no advantage pertaining to physical quality characteristics of importance in an ostrich abattoir. <![CDATA[<b>Effect of location of eggs in the incubator on hatchability of eggs from Bronze turkey breeders of different ages</b>]]> The objective of this study was to determine the effect of location in an incubator on the hatching characteristics of eggs obtained from Bronze turkeys of different ages, viz. at the ages of 8, 10 and 12 months. In the study 330 eggs were placed in each of six locations within an incubator, totalling 1 980 eggs from each age group, and 5 940 eggs overall. The highest fertility rate and hatchability of all eggs set, and of fertile eggs were recorded in the eggs from 10-month old breeders. The lowest rates of shell adhesion deaths, null poults and poults with abnormalities were also observed in this group. In all age groups investigated, the hatchability of all eggs set and of fertile eggs was the highest in eggs placed in the front of the machine. Furthermore, early and middle stage deaths during incubation were lower in the front of the incubator compared to the back. The differences between eggs placed in the upper, middle and lower parts of the machine with respect to the investigated characteristics were not statistically significant. Although these results were obtained from a specific incubator, the locations inside and all applications (temperature, humidity, shaking, etc.) were within accepted standards. Therefore, results are applicable, in general. <![CDATA[<b>Effect of dietary mannan oligosaccharide with or without oregano essential oil and hop extract supplementation on the performance and slaughter characteristics of male broilers</b>]]> The effects of some alternative feed additives for antibiotic growth promoters on performance and some slaughter characteristics were examined in broilers fed wheat-soya based basal starter and finisher diets. A total of 2160 one-day-old male broiler chicks were randomly allocated to six groups with six replicate pens per treatment. The treatments were the basal diet (Control), and the basal diet supplemented with an antibiotic growth promoter (AGP); a prebiotic, mannan oligosaccharide (Bio-Mos, MOS); an essential oil of oregano (Herb-Mos Oregano, HMO); a plant extract of hop (Herb-Mos Hops, HMH) or a mixture of Herb-Mos Oregano and Herb-Mos Hops (HMOH). There were significant effects of dietary treatments on body weight and feed conversion ratio in the 0 - 21 d period, and on body weight and feed consumption in the 0 - 42 d period. The addition of all experimental additives to the diet resulted in significantly higher body weights as compared to the control treatment at both 21 and 42 days of age. Feed intakes were significantly different between the treatments at 0 - 21 d and 22 - 42 d periods, but not during the 0 - 42 d period. However, during the 0 - 21 d period the broiler chickens that received diets supplemented with AGP, MOS, HMO, HMH and HMOH had significantly better feed conversion ratios than the control group, but this pattern was not sustained during the finisher period (22 - 42 d). Mortality rate, hot carcass yield and relative weights of the small intestines, pancreas, abdominal fat and bursa of fabricius were not affected by experimental treatments. The HMH supplementation increased relative liver weight. These results showed that AGP, MOS and herbal feed additive (HMO, HMH, HMOH) supplementation to a diet provided significant advantages on broiler growth performance through a 42-d growth period. However, the combined supplementation of HMO and HMH did not exert either synergistic or additive benefits on the live performance of the broilers. These results also proved that MOS, HMO, HMH and HMOH improved broiler live performance as well as an AGP in both the starter and through the grower period. Furthermore, outstanding advantages were evidenced for the HMH treatment in particular. Therefore, the MOS, HMO, HMH and HMOH performance enhancer feed additives of natural origin may be considered as potential substitutes for AGP in broiler diets. <![CDATA[<b>The influence of fat score and fat trimming on primal cut composition of South African lamb</b>]]> The objectives of this study were to evaluate the primal cut composition of South African lamb carcasses with different fat scores, and to identify cuts suitable for fat trimming. Sixty grain fed Dorper lambs (rams and ewes) were divided into three groups and slaughtered at 30, 36 and 42 kg. Chilled carcass sides were subdivided into seven primal cuts. The cuts were dissected into meat (muscle, intermuscular and intramuscular fat), bone and subcutaneous fat (SCF) in order to determine the physical composition per cut and for the whole carcass. The % subcutaneous fat (SCF) in the loin increased the most (26 units) as the fat score increased from 1 to 5, followed by the flank, shoulder and neck. The % meat (lean) of the neck, thick rib and breast showed no significant change between fat scores 1 to 5, while % bone decreased significantly (>6% units). Meat and bone proportions decreased significantly with an increase in fat score for the loin, flank, leg and shoulder. The composition of the loin cut was most affected overall by changes in the fat score. Since different cuts accumulate SCF at different rates during fattening, trimming of SCF could reduce the boneless % SCF level of the major cuts such as the loin, leg and shoulder by 12, 6 and 9 units, respectively, when trimmed from SCF equal to a fat score 5 to a fat score 3. Further trimming to levels equal to a fat score 1, could reduce the % SCF by 18, 8 and 5 units, respectively on a boneless level. Considering differences in relative increase in intermuscular fat (IMF) and SCF in different cuts, the leg seems to be the most suitable cut for trimming in fat carcasses, since the IMF : SCF ratio is the lowest compared to the other larger cuts namely the loin and shoulder. <![CDATA[<b>Comparative digestive ability and rumen microbial community of N'Dama and N'Dama x Jersey cattle fed different diets</b>]]> Rumen fluid collected from three rumen fistulated N'Dama and three crossbred animals fed three different diets at medium supplementation level, was used to compare the plant cell wall degrading community of the two breeds of cattle. In vivo digestibility was also examined and compared using 12 animals (six of each breed) fed the same diets. The microbial community of the rumen was analyzed by 16S rRNA hybridisation, using phylogenetic probes of different levels: a universal probe, domain-specific probes for Bacteria, Eukarya and Archaea, and probes targeting cellulolytic organisms: Chytridiomycetes, Fibrobacter spp., Ruminococcus albus and Ruminococcus flavefaciens. In vivo, organic matter (OM) and neutral detergent fibre (NDF) digestibility were significantly higher in N'Dama compared to crossbred animals when they were fed either baby corn stover and concentrate, or groundnut hay and moringa. In contrast, when the animals were fed groundnut hay and concentrate there was no difference in OM and NDF digestibility between the two breeds. Results of the microbial community analysis showed that RNA concentration of total Bacteria and Archaea was not affected by the breeds of animal, but were significantly affected by diet. The eukaryotic RNA concentration was higher in crossbred animals compared to the N'Dama and was not affected by the diet. Fibrobacter and R. flavefaciens RNA concentrations (µg/mL) were significantly dependent on diet and breed. Ruminococcus albus and Chytridiomycetes RNA concentrations were neither affected by the breed, nor by the diet of the animals. This suggested that the differences between breeds observed in digestibility could be partially explained by the composition of the cell wall degrading community.