Threonine and lysine requirements for maintenance in chickens

In order to describe the response of broiler breeder hens to dietary amino acids and to develop an effective model for the precise feeding of these birds after sexual maturity, accurate estimates of the amounts of each amino acid required for maintenance and egg production are needed. The maintenance requirement for threonine and lysine were estimated in two different experiments by measuring the nitrogen balance of adult male cockerels. Measured amounts of a diet first-limiting in threonine or lysine were fed by intubation each day for 4 d to give a range of intakes (unbalanced series) of from 0 to 239 mg threonine/kg or 0 to 40 mg lysine/kg body weight. To confirm that threonine or lysine was first-limiting and that the response obtained was to threonine or lysine and not to protein, a second series of diets was used (balanced series) in which synthetic threonine or lysine was added to each diet in the unbalanced series. A nitrogen-free diet containing energy, vitamins and minerals was made available ad libitum during the balance period, to ensure that the birds remained in positive energy balance. The balance period was three days and excreta were collected in colostomy bags (threonine) or in trays (lysine) during that time. The nitrogen content of the excreta was determined on dried homogenised samples. The resultant linear regression equations describing the effect of threonine or lysine intakes on nitrogen retention were: N retention = -230.4 (± 27.6) + 4.134 (± 0.274) I (R2 = 91.9) and N retention = -256.8 (± 37.7) + 6.89 (± 1.37) I (R2 = 70.8), respectively, where I is the intake of threonine or lysine in mg/kg body weight day. The threonine and lysine required to maintain the body at zero nitrogen retention was therefore estimated to be 56 and 37 mg/kg body weight day, respectively. Keywords: Maintenance requirements, amino acids, cockerels South African Journal of Animal Science Vol. 38 (2) 2008: pp. 75-8

Effect of dietary protein content on growth, uniformity and mortality of two commercial broiler strains

Two experiments were conducted to determine the response in performance, including uniformity and mortality, of two broiler strains to dietary protein content. In Experiment 1, 480 Cobb 500 and 480 Ross 788 day-old sexed broiler chickens were housed in cages to 21 d with 10 chickens per cage, and in Experiment 2, lasting 42 d, 1680 sexed broiler chickens of each of these two strains were placed in 48 floor pens with 70 chickens per pen. Males and females were reared separately in both experiments. Six levels of dietary protein were fed for 21 d in both experiments, the composition changing for the period 22 to 42 d in Experiment 2. Body weight of each bird was measured at weekly intervals up to 21 d in Experiment 1, and of 20 randomly selected birds from each pen on days 1, 21 and 42 in the second experiment. Broilers in the latter trial were group-weighed by pen at weekly intervals. Mortality was monitored daily. The highest body weight gains and feed conversion efficiencies (FCE, g gain/ kg food) were recorded in Cobb, with a correspondingly higher food intake for the starter feed in both experiments. In the finisher period Ross birds consumed significantly more than Cobb broilers (9 g/d) but in this case there was no difference in growth rate between the two strains, resulting in a significantly poorer FCE for Ross (487 vs. 522 g gain/kg feed). The pattern of food intake in the finisher period also differed between the two strains: the Cobb birds increased their food intake as the dietary protein content was decreased, but food intake decreased with protein content in the Ross. Uniformity was greatest in both strains when they were fed the highest protein feeds in both experiments, the variation in live weight increasing as the protein content decreased. There was no nutritional effect on mortality, although mean overall mortality was twice as high in Cobb broilers. Keywords: Broiler, strain, uniformity, mortality, dietary protein South African Journal of Animal Science Vol. 38 (4) 2008: pp. 293-30

Broiler breeders should not be reared on long photoperiods

Sexual maturity is delayed and egg numbers are reduced when broiler breeders are reared on long photoperiods. However, this is the recommended procedure for rearing spring-hatched birds in non-lightproof buildings. Research at the University of KwaZulu-Natal has suggested that this advice may be incorrect, and that precocity is not a problem in control-fed broiler breeders reared on increasing daylengths. This trial compared the responses of four broiler breeder genotypes to a typical lighting programme advocated for birds in lightproof housing with the provision of 14-h photoperiods to 20 weeks and 16 h in lay. The long-day rearing resulted in a 26-d delay in sexual maturation, seven fewer eggs to 60 weeks, a 2.5-g increase in egg weight, less efficient feed conversion, heavier body weights at sexual maturity and throughout the laying period, and a higher incidence of mortality. It is concluded, therefore, that broiler breeders should not be reared on long photoperiods, even when hatched in the spring and kept in non-lightproof facilities, because of the adverse consequences of a delay in the dissipation of photorefractoriness. Keywords: Broiler breeder; light, rearing; long days; out-of-season South African Journal of Animal Science Vol. 37 (4) 2007: pp.215-22

Abrupt or gradual increases in photoperiod for broiler breeders

Cobb 500 broiler breeder females (n = 832), which had been raised to achieve a typical 20-week body weight of 2.1 kg, were subjected to an abrupt or gradual increase in photoperiod to determine the effects on reproductive performance. One group (n = 416) was reared on 8-h photoperiods till 19 weeks and abruptly transferred to 16-h photoperiods. Another group (n = 416) was reared on 8-h photoperiods and given an initial increase to 12 h at 19 weeks, then weekly increments of 1 h to reach 16 h at 23 weeks. Both groups were reared in light-proofed facilities to 23 weeks and then moved to curtain-sided housing and maintained on 16-h daylengths to 60 weeks. There were no significant differences between the two lighting groups for age at sexual maturity, total egg production, egg mass output, mean egg weight to or body weight at 60 weeks. However, the birds given a single abrupt increment had a higher peak rate of lay whilst those given a gradual increase in daylength had better egg production at the end of the laying cycle. Broiler breeders transferred from closed rearing to curtain-sided adult accommodation (similar to that in which a large proportion of broiler breeders are housed) respond similarly to abrupt and gradual increases in daylength as do birds maintained throughout in controlled environment accommodation, and modern genotypes have similar responses to early genotypes. South African Journal of Animal Science Vol. 36(1) 2006: 45-4

To what extent can the age at sexual maturity of broiler breeders be reduced?

Two trials were conducted to investigate the effects of growth manipulation and early photostimulation on age at sexual maturity and, in one trial, subsequent laying performance, in broiler breeders. In the first trial, the possibility of reducing the age at sexual maturity, using early photostimulation and increasing the growth rate to achieve 2100 g at 15 weeks, was assessed. Sexual maturity was advanced by 15 d and the total number of eggs laid to 60 weeks, on a hen.week basis, was reduced significantly, by six. Mean egg weight was unaffected, but the number of unsettable eggs was increased by 2.6. Using 12 h rather than 16-h daylengths during the laying period resulted in a significant increase (7) in number of eggs laid. In the second trial, birds were transferred from 8 to 16-h daylengths at 10, 11, 12, 14, 16 or 18 weeks to determine the age at which they were able to dissipate photorefractoriness, and become photosensitive. Short-day controls were maintained on 8-h daylengths throughout. Birds were grown to achieve 2100 g at either 15 or 20 weeks. No interaction occurred between age at photostimulation and body weight. Because broiler breeders exhibit photorefractoriness, the earliest age at which the pullets responded to photostimulation was 14 weeks, so no advantage would be gained in terms of advancing sexual maturity by photostimulating earlier than this age. However, whilst some further advance in sexual maturity may be achieved by rearing the birds on a faster growth curve this would only be profitable through the advantages of being able to use one rearing unit to service three, instead of two, laying farms. Keywords: Broiler breeder; photostimulation; growth curve;sexual maturity;egg production South African Journal of Animal Sciences Vol. 35 (2) 2005: pp.73-8

Male broiler performance and nocturnal feeding under constant 8-h or 16-h photoperiods, and various increasing lighting regimens

This paper describes the responses of two genotypes of male broilers to constant 8- and 16-h photoperiods, and to an abrupt transfer from 8 to 16 h at 10, 15 or 20 d. Body weight, feed intake, and feed conversion efficiency were not significantly different at any stage during the 35 d study. Mortality and the incidence of Sudden Death Syndrome were similar for all lighting groups at 35 d. When these data were pooled with previously reported data for female broilers, growth and feed conversion efficiency post 21 d and through to depletion for constant 8-h and birds transferred from 8 to 16 h at 20 d were significantly superior to constant 16-h birds. Constant 8-h birds ate about half their feed during the dark period, whilst 16-h birds consumed no more than 10%. Birds which had been started on 8 h and transferred to 16 h at 10, 15 or 20 d reduced their rate of nocturnal feeding when changed to the longer photoperiod, however, they still consumed more feed in the 8-h dark period than birds that had always been given 16 h illumination. Cobb and Ross genotypes responded similarly to all lighting treatments. Keywords: Photoperiod, broiler growth, nocturnal feedingSouth African Journal of Animal Science Vol. 38 (3) 2008: pp. 159-16

Supplementary radio noise advances sexual maturity in domestic pullets exposed to 7-h photoperiods

Cage-reared, egg-type domestic pullets were given a 7L:17D regimen from 2 d of age. At eight weeks, 24 birds were transferred to individual cages in each of four controlled environment chambers and maintained on 7-h photoperiods. A radio was played at 75-80 dB from 10 weeks of age in two of the chambers during the 7 h immediately preceding the photoperiod, and the other two chambers remained as controls. Mean age at first egg for the radio birds (143 d) was 13 d significantly earlier than controls, but body weight at first egg was similar for the two groups. Although this suggests that the radio noise might have stimulated feeding activity and accelerated growth, there was no significant difference between the groups for a regression of body weight on age at first egg, indicating that accelerated growth did not contribute to the advance in maturity. A shift in the location of the photoinducible phase, so that it became partially illuminated by the normally non-stimulatory 7-h photoperiod, is another possible reason for the earlier sexual development. Plasma melatonin concentrations midway through the 7-h dark period in which the radio was played were similar to those of non-radio controls, indicating that this period was not regarded as being part of a 14-h subjective day. Keywords: Environmental cue; sound; sexual maturity South African Journal of Animal Sciences Vol. 35 (3) 2005: pp.180-18

Simulated natural lighting and constant 14-hour photoperiods for broiler breeders during the rearing period, and interactions of lighting with body weight

No Abstract. South African Journal of Animal Science Vol. 35 (1) 2005: pp.1-1