Effect of high energy diets on the productive and reproductive characteristics of young Bonsmara bulls

• Main Author: Labuschagné, Hermanus Stefanus
• Format: Others
• Language: English
• Published: Port Elizabeth Technikon 2001
• Subjects: Bonsmara cattle
• Online Access: http://hdl.handle.net/10948/58

A study to evaluate the effect of feeding a high energy diet on the productive and reproductive characteristics of young bulls was carried out at two different locations in the Free State Province. Two trials were conducted with the aim of evaluating the effect of level of dietary energy and age of the bulls on their productive performance and reproductive characteristics. In the first trial, two levels of energy were fed to two groups of young (343 ± days) Bonsmara bulls. The high energy group HE (n=36) bulls were Phase-C performance tested in an official performance testing center and received a high energy diet for 112 days (28 days adaptation and 84 days testing). The medium energy group ME (n=18) bulls were phase-D performance tested and received a medium-energy diet for 140 days (28 days adaptation and 112 days testing). At the end of both performance testing periods, the productive performances and reproductive characteristics of the two groups were compared. The productive parameters compared included final live body weight (FLW), average daily gain (ADG), average daily gain per day of age (ADA) and body condition score (BCS). The reproductive parameters compared between groups included scrotal circumference (SC), semen volume (Vol) and concentration (SConO), mass movement (MV), linear motility (LM), percentage live sperm (LS), as well as percentage of total abnormalities: major (MD) and minor (MinD). The results of this trial indicated that in general, bulls from the HE group showed a significant (p<0.01) higher FLW, BCS, ADG and ADA, but a significant (p<0.01) lower volume and concentration of the ejaculate, lower mass movement and linear motility, lower percentage of live sperm and higher percentage of major defects and significantly (p<0.05) higher percentage of minor defects than the bulls from the ME group. In the second trial, 36 young Bonsmara bulls were divided into two groups according to their age at the arrival at an official Phase-C performance testing center. Older bulls (OB) (n=19) and younger bulls (YB) (n=17) all received a high energy diet for 112 days (28 days adaptation and 84 days testing). At the end of the Phase-C test the productive performances and reproductive characteristics of the two groups were compared. The animals from both groups that did not pass the Phase-C test, either due to poor performance or not meeting the breed standards, were slaughtered at an official abattoir and their scrotums and carcass characteristics were also compared. The productive parameters compared between the two groups included final live body weight (FLW), average daily gain (ADG), average daily gain per day of age (ADA), body condition score (BCS), feed conversion ratio (FCR), carcass weight both warm (CWW) and cold (CWC), as well as dressing percentage (CDP) and fat grade (CFG). The reproductive parameters compared between the two groups included scrotal circumference (SC), total scrotal weight (TSW), scrotal fat (SF), scrotal skin weight (SSW), paired testes weight (PTW), scrotal skin thickness (SST), total testes circumference (TTC), total testicle volume (TTV), weight of epididimis / spermatic cord (WESC), volume of epididymis / spermatic cord (VESC) and the percentage of bulls with depressed spermatogenesis (PBDS), semen concentration (SConO), mass movement (MV), linear motility (LM), percentage live sperm (LS), percentage of total abnormalities: major (MD) and minor(MinD) as well as the percentage of bulls with depressed spermatogenesis (PBDS). The results of this trial indicated that in general, the younger bulls showed a significant (p<0.05) higher ADG, but a significant (p<0.05) lower ADA than the older bulls. Regarding the reproductive organs compared, the younger bulls showed a significantly (p<0.01) higher total scrotal weight, scrotal fat and scrotal skin weight and thickness. No significant differences were observed on the testicular parameters measured between the two groups. In addition, both weight (WECS) and volume (VECS) of the epididymis / spermatic cord were significantly (P<0.05) higher in the older bulls. In general, the younger group showed poorer semen characteristics. A significantly (p<0.01) lower sperm concentration and linear movement and a significantly (p<0.05) higher percentage of major defects were recorded on the younger bulls, when compared to the older bulls. About half of the bulls in each group showed clear signs of depressed spermatogenesis in their seminiferous tubules, during the histological examination of testicular tissue. The results of this study indicates that high energy diets are beneficial for the productive performance of young bulls (growth rate, BCS and carcass characteristics), but have a detrimental effect on the reproductive characteristics of young bulls. The effect of high energy diets on both the productive and reproductive performances of young beef bulls are more pronounced at a younger age. High energy diets resulted in heavier scrotums in the younger bulls when compared to the older bulls, as a direct result of a higher fat deposition in this region without any relevant effect on testicular size. No intra-testicular fat deposition was observed. The scrotal fat observed in high energy fed young bulls accumulated mainly in the neck of the scrotum, although subcutaneously. These fat deposits may impair testicular thermoregulation and negatively affect the spermatogenesis in the seminiferous tubules, reducing both sperm quantity and quality. Further studies on the effect of high energy diets on bull fertility (as well as on rams and buck) are recommended, to evaluate the extension and duration of its detrimental effects on subsequent fertility.