ABSTRACT The current study was conducted to investigate the influence of provitamin A biofortified maize (PABM) diet, sex and age of birds on the haematological and serum biochemistry parameters of indigenous chickens. A total of ninety-six 13 week old male and female Ovambo chickens were reared and fed on either white maize (WM) a low vitamin A diet or a PABM based diet for eight weeks. Each diet was replicated four times. Packed cell volume (PCV), haemoglobin (Hb), erythrocyte concentration (RBC), leucocytes concentration (WBC), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH) and mean corpuscular haemoglobin concentration (MCHC) were measured. Albumin (ALB), globulin (GLOB), total proteins (TP), triglycerides (TRI), cholesterol (CHOLES), uric acid (UA) and creatinine (CREAT) concentrations were assessed. The activity of alanine transaminase (ALT) alkaline phosphate (ALP) and aspartate transaminanse (AST) were also assayed. The PABM diet increased (p<0.05) PCV and WBC of female birds. All mean values for the haematological parameters regardless of the age, sex and diets were within the normal range. Age had an effect (p<0.05) on ALT, TP, GLOB, TRI and UA. Sex of the birds significantly influenced the TP, GLOB, ALB, CREAT and TRI levels. There was significant interaction of diet and age of bird on ALP, ALT, and GLOB concentrations. The cholesterol level in 18 weeks old male birds fed on the WM diet was above the normal range. In conclusion, feeding PABM diet to female and male indigenous chickens will not negatively impact on the health status of indigenous chickens.

ABSTRACT Free-range chicken production has significantly increased in recent years and it often entails exposing birds to cyclic environmental conditions. The objective of the current study was to investigate the effect of bird strain and sex, and rearing system on the physiological responses of Potchefstroom Koekoek (PK), Ovambo (OV) and Naked Neck (NN) chickens reared in a hot environment. Body weight (BW), rectal temperature (RT), respiratory rate (RR) and heart rate (HR) were determined weekly for 4 weeks, in 3 slow-growing chicken strains under cyclic environmental conditions. A total of 288, 20-week old Potchefstroom Koekoek (PK), Ovambo (OV) and Naked Neck (NN) chickens were separated by sex and allocated to extensive and intensive rearing systems. Ambient temperature and relative humidity (RH) were used to compute a temperature humidity index (THI). A Proc MIXED model was used to analyze fixed effects and a linear regression model was fitted to test the relationship between THI and response parameters. All factors studied influenced (p<0.05) BW while none affected (p>0.05) RT. Higher BW (p<0.05) were obtained with OV in both rearing systems. Sex influenced (p=0.0021) HR but not RR (p>0.05). Week and rearing system affected (p>0.05) RR. THI showed significant correlation with RR and HR. THI was higher in intensive than extensive rearing. Physiological responses of PK, OV and NN are comparable under similar rearing conditions.

ABSTRACT The study was conducted to determine the interaction of types of maize (Provitamin A-biofortified maize (PABM) versus white maize) and strain of laying birds (Amberlink and Hyline) on nutritional quality of eggs. Twenty-one of each of Amberlink and Hyline laying hens were fed on three diets for 30 days. Birds were distributed in a 3 × 2 factorial arrangement constituting three diets (0, 50 or 100 % of PABM) and two strains (Amberlink & Hyline). There was a diet × strain interaction on egg shell weight, average daily feed intake, egg production, egg weight and egg shell thickness. Eggs produced by layers under 100 % PABM had lighter eggshell weight and lower eggshell percentage. In contrast, eggs produced by layers under 50 % PABM diet had signi-ficantly higher eggshell percentage, heavier egg shell weight and thicker eggshell. As the level of PABM increased, the yellow and red hue (Hunter a* and b* values) significantly increased while the lightness values (Hunter L* values) decreased. As the level of PABM in the ration increased, the vitamin A content of the egg yolk also significantly increased. Assimilation of vitamin A from feed to egg yolk in Amberlink and Hyline hens was similar. Hence, egg enrichment with vitamin A can be achieved by using PABM in layers ration. The use of high level of PABM had a negative effect on the eggshell quality traits.

Within-litter birth weight variation in pigs is increasingly becoming important in influencing the profitability of pig enterprises. The objective of the study was to characterize within-litter birth weight variation in piglets from Large White χ Landrace sows. The study was conducted using records from 1 768 litters collected between January 1998 and September 2010 from a pig herd in South Africa. The number of piglets born alive (NBA) ranged from three to 18. The mean within-litter birth weight coefficient of variation (CVBWT) was 17.6% and ranged from 0.47% to 50.7%. The distribution of CVBWT in the herd was positively skewed. CVBWT increased as NBA increased. Multiparous sows farrowed litters with higher CVBWT than gilts. To enhance profitability of pig enterprises, the selection for increased NBA should be followed by selection for decreased CVBWT.

Genetic evaluation of dairy cattle using test-day models is now common internationally. In South Africa a fixed regression test-day model is used to generate breeding values for dairy animals on a routine basis. The model is, however, often criticized for erroneously assuming a standard lactation curve for cows in similar contemporary groups and homogeneity of additive genetic variances across lactation and for its inability to account for persistency of lactation. The random regression test-day model has been suggested as a more appropriate method and is currently implemented by several Interbull member-countries. This review traces the development of random regression methods and their adoption in test-day models. Comparisons are drawn with the fixed regression test-day model. The paper discusses reasons for suggesting the adoption of the random regression approach for dairy cattle evaluation in South Africa and identifies the key areas where research efforts should focus.