Selection for improving feed efficiency
There is a constant stress on lowering the cost of production of chicken. This can be achieved by increasing the body weight or by reducing the major input ‘feed’. Body weights are improving resulting in reduction of slaughter age by one day every year. Further economic advantage can be achieved by reducing the feed consumption per unit of chicken produced.
Individual feed consumption is measured on 7097 pedigreed broiler stocks under a sire testing programme from 28 to 42 days. Genetic parameters for wt28d, wt42d, wt gain and feed consumed are calculated. Efficiency of individual selection based on various weights feed measurements and a combination of them on all the characters involved are studied. A combination of Weight and feed measurements seems to be more useful when compared to either one of them. The efficiency of three indices in this direction is examined.
Materials and Methods
Individual cage facility is provided with specially designed single bird feeders. Electronic balances are used to weigh feed and birds up to one gram accuracy. The birds under study are male line broiler birds produced under a sire testing programme. 7097 birds belonging to 460 sires produced in 6 flocks at different periods of the year form the basis for this study. The birds are selected at 28 days and 50 to 70% of the birds are shifted with in 4 hours after weighing in to single cages. The males were heavily selected and are fewer in number. Hence only female data is considered. The mortality after caging was negligible (less than 0.3%). Obvious abnormal data records were taken out of the analysis.
The heritabilities, genetic and phenotypic correlations are calculated by analysis of variance. All the estimates are based on sire component of variance. Different selection criteria are tried. The ultimate response depends on heritabilities, selection differentials and the correlated response in the related traits depending on the genetic correlations. Actual selection differential is taken as an indicator to measure the efficiency of the selection criterion while the genetic parameters are the same.
The different selection criterions tried are mass selection for a single trait. Same numbers of birds are selected from the population based on either wt28d or wt42d or wt gain or feed consumed separately. FCR is calculated as a ratio –feed consumed/wt gain. The feed utilized for body growth and maintenance is statistically calculated. The difference of feed between feed consumed and this is arrived at as residual feed consumption.
The following combinations of traits as indexes are tried.
Pym Index is calculated as index = wt42d-0.3*feed consumption – 0.5*wt28d as suggested by Pym of queens land Australia (1996).
A linear index is calculated by using feed consumed and wt42d. The chicken price is three times higher than feed prices. Hence the economic values are taken as –1 for feed consumed and 3 for wt42d. The final index worked out was index = -0.142*feed consumed +0.411*wt42d.
An index combining wt28d and residual feed consumption as suggested by Dr. Jain (1996) is examined.
Index = standard normal deviation on wt28d-standard normal deviation of residual feed consumption
The selection differentials in all the characters are calculated every time for comparison.
Results and Discussion
The mean values for the parameters are presented in table-1.
Table-1 Mean values for various traits
There is variation in all the parameters from season to season. Feed consumption and body weights are more during the winter months and were low during hot months. This expected.
The FCR figures appear higher compared to industry data. The figures are based on females only. Only starter feed with an energy level of 2740 is given and the FCR covers the later part of broiler growth curve and does not include the earlier portion where the FCRs are low.
The heritabilities presented in table –2
Table –2 Heritabilities and correlations
Figures on the diagonal are h 2 above rG and below rP.
The estimates presented are on a lower side of the figures presented in the literature. Most of the flocks have been under constant selection. The data includes only selected birds at 28 days, which could have influenced the estimates to some extent. To know the effect of selection, the estimates on wt28days, wt42days and wtgain were obtained on one full flock to know the difference. The estimates were found to be low when only selected birds data is used. The estimated obtained on all the birds living at 42days, the caged birds from the same flock and pooled data on selected birds only for all the three hatches in a particular flock are presented in table-3
Table-3 Parameters as influenced by flock size
The correlations between wt28d and wt42d are positive and high. The correlation with wt42d is higher than with wt28d (almost double). Both phenotypic and genetic correlations of FCR with wt42d and wt gain are negative (favorable) and strong. The correlation is even higher with wt gain compared to wt42d. The correlation of FCR with wt28d is positive (unfavorable) though low. This might make lot of difference in the ultimate profitability if the selections were to be finalized at 28days under the assumption of positive correlation between wt28d and wt42d.
The heritabilities of feed consumption, residual feed consumption and FCR are lower than the estimates reported.
The selection differentials on various selection criteria are presented in table-4.
Selection based on wt28D – Is expected to improve the wt28d fastest but the FCRs at 42d would be the worst when compared to other criteria may be practiced if the targeted market is 1200gms slaughter at about 30days of age. Caution has to be exercised for a larger bird market because of loosing FCRs. The second concern would be mortality that would go up at the later age which will add to the poor FCRs. The mortalities could be due to two reasons. One, the varying climates like sudden raise in day temperatures where an early fast growing birds suffer more. Second, because of the capacities of the organs in the early heavy broilers being disproportionately lower to body size. There is a growing concern about the problems like sudden death syndrome and gout. These problems are due to inability of the heavy body at an early age to handle the extra requirement of oxygen with change of climate or extra excretory capacity of the kidney required to handle the high protein diet that is being given now a days right from day one. May be the development of the organs like lung, heart and kidney are not proportionate to the development of the body tissues happening with selection.
Selection based on wt42d – results in highest gains for wt42d. We can expect a favorable response in feed efficiency also. Selection for 42d improves wt28d also but not to an extent as would happen in case of direct selection for wt28d.
Selection based on wt gain directly seems to be more use full tool when compared to both the above to improve FCR. the very measurement of this trait involves two weighing in the programme. The other caution to be exercised is that weight gain can result from reducing wt28d, not necessarily by increase in wt45d if we do not keep an eye on wt45d which is the ultimate selling point.
Direct selection for FCR – gives the best possible selection differential for FCR, if other characters are not to be considered. It can be noticed that the mediocre birds are the most efficient on conversion. The small bodied birds require less feed for maintenance and may be having less appetite to avoid extra residual feed. This observation coincides with the reports published in literature. Measurement of individual feed consumption has to be done in any case.
Combined selection – Two measurements on body weights and feed consumption seems to be inevitable in present day market where feed is expensive and the producer is looking for a bird that converts the feed more efficiently.
Once the wt28d, wt42d and feed consumed are measured, intelligent statistical manipulations can be attempted to get the extra gains. The selection effect of the combined selection is definitely providing balanced gains in wt28d, wt42d, wt gain and FCR. all the three indexes seem to be alright in the direction of increasing the wt gain and reducing the FCR. the magnitude, if considered real, one can decide on the use of one of the indexes based on his need. If the need is to catch up with wt42d, which is more important to sell chicks, the third index gives faster gains in weights and still with gains in FCR. If the weights are competitive and one has to improve on FCR, index 1 and 2 seems to be use full.
Summary and Conclusions
Selection for feed efficiency is inevitable in the present market. Two weights w28d, w42d and individual feed offered and balance feed were measured. Wt gain, feed consumed, FCR and residual feed figures are calculated. Selection at an early age could be dubious in respect of FCR and probable mortalities. Selection for the same weights the market requires seems to be the fastest way to achieve the wt42d if other things are ignored. Direct selection for FCR improves FCR but may not improve weights. Balanced economic gains can be obtained by an index combining both feed measurements and weight measurements. The weight ages to be given are to be judged by the current status of the stocks.
|Source : IPSACON-2005|