- To examine how the timing of increases or reductions in dietary protein affect growth and breast muscle deposition. This will determine if more heavily fleshed birds maintain breast muscle tissue at the expense of egg production.
- To characterize the physiology of the reproductive response (reproductive maturation, egg production traits, duration of fertility and hatchability) under normal and alternative protein intake conditions.
- To use early and standard photostimulation ages to identify how protein intake patterns during rearing impact reproductive readiness.
- To identify early indicators of metabolic and reproductive dysfunction. Can markers such as relative chick body weight, breast muscle fleshing, age at sexual maturity, and ovarian morphology be used to effectively predict reproductive potential?
- To trace changes in weight and fleshing measurements of all birds in commercial broiler breeder flocks and to relate these changes to the health, livability and reproductive status of birds at the end of lay. Is there an ideal juvenile growth profile for long-term reproductive effectiveness in a commercial setting?
BackgroundThere is a large variation in laying performance of commercial broiler breeder chickens, both among strains and among different producers. Careful management decisions are required, especially during sexual maturation, to maximize egg production. This project builds on years of work done at the University of Alberta towards a better understanding of the interaction between protein intake and reproductive efficiency in broiler breeders. This work has been especially enlightening as it creates profiles of these interactions for individual birds rather than looking at whole flock responses.
The overall objective of this research program is to determine the impact of varying protein intake patterns of broiler breeder females during the growth phase on carcass traits and reproductive potential and use this information to create a growth profile that can help predict future performance.
Research ProgressThe main research flock related to this experiment consisted of 600 Ross 308s and 600 708s. During their growth phase, the birds were fed either a standard breeder ration or one that was 3% higher or 3% lower in dietary balanced protein (rations were balanced in the top 14 amino acids to avoid confounding results from limiting amino acids). The high or low protein rations were fed over 1 of 4 time periods: 1-7, 7-13, 13-19 or 19-25 weeks. Feed allocation was the same in the three feeding treatments. Birds were fed ad libitum for 2 weeks, then were on a 5 of 7-day feed restriction program, then fed daily from 17 weeks of age on. Various measures were taken throughout the experiment (body weight, external carcass characteristics, breast yield, fad pad weight, liver weight, reproductive development). As expected, the 308s were heavier overall and the 708s produced a higher percentage of breast yield. There were only minor diet effects on the birds prior to sexual maturity. At 17 weeks, a subset of birds was moved to individual cages. The 308s reached sexual maturity earlier. It was unexpected that changes to dietary protein during the 1 to 7 wk period (when early frame size set) and during the 19 to 25 wk period (when reproductive tract developing) did not affect reproductive or carcass traits at sexual maturity. Carcass traits at sexual maturation were most affected by changes in dietary protein during the 13 to 19 wk period. The 7 to 13 wk dietary protein level influence on subsequent ovary traits at sexual maturity is the earliest demonstration of nutrition on the ovary – which is normally immune to changes prior to 14 wk of age. Although statistically significant, the differences were not large. The importance of the results exist in the fact that a 3% change in dietary protein can continue to have an effect long after the point in rearing it was given. These results suggest that feeding a high protein diet during the growth phase may not be necessary for good reproductive development.
The true impact of a treatment is on the long-term reproductive traits – egg and chick production. Dietary protein levels had minor effects on egg production. Neither the total eggs laid nor the number of settable eggs was significantly influenced by diet. Feeding the LOW diet to young pullets (1-7 wks) led to production of the most small eggs. Feeding the HIGH diet later on (13-19 wks), especially close to sexual maturity (19-25 wks), resulted in the lowest fertility. Both the 308s and the 708s performed well on the standard diet. Ultimately chick production was reduced by altering the dietary protein during rearing. This effect was most pronounced early in lay. Hatchability in early production (31 to 42 wk of age) was 89% in control birds vs. 82% and 85% in HIGH and LOW dietary balanced protein groups, respectively. Birds receiving additional protein at some point during the rearing phase ultimately produced 8 fewer chicks than hens on the standard diet Control treatment.
In a related trial, chicks were fed ad lib for either 1 or 3 weeks. Growth curves thereafter were designed to merge the 2 groups by 10 weeks of age. As expected, the 3WK group initially gained much more weight, but upon being feed restricted virtually matched the other group in all respects, including apparent reproductive development, by the end of the trial (16 weeks). Flock uniformity was better for the 1WK group, presumably due to the easier transition into feed restriction and less competition for feed from aggressive birds. The pullets were photostimulated at 17, 19, 21 or 23 weeks. As expected, stimulating birds later resulted in delayed onset of sexual maturity, but these birds matured more quickly than those photostimulated early. Flocks stimulated later came into lay most consistently and had larger early eggs. These results suggest that more mature birds can better respond to photostimulation cues.
Data were also collected on 2 commercial breeder flocks from hatch to end of lay. Chick size had little correlation to production traits while measurements at 9 weeks were more predictive. On average, lighter birds had fewer large yellow follicles (LYFs) in their ovary and a higher percentage of them were out of lay. Everting the cloaca, as is done during artificial insemination, was used to indicate if a hen was laying or not. Heavy birds, on the other hand, tended toward more LYFs (too many LYFs can result in double-yolked eggs and other reproductive problems).
Future WorkThe results continue to be analyzed in the context of the overall breeder physiology program. As the broiler breeders of the future continue to improve their growth and breast muscle deposition potential, protein delivery may start to play a more important role and warrant rethinking how we grow our breeding stocks. This project has identified some of the issues we will face.
Funding$149,400 (CPRC $19,000, AARI $90,000, Aviagen $35,000, Aviagen (in kind) $5,400)
PublicationsPishnamazi, A., R. A. Renema, M. J. Zuidhof, and F. E. Robinson, 2008. Effect of initial full feeding broiler breeder pullets on carcass developmentand body weight uniformity. J. Appl. Poult. Res. (Submitted for Publication).