Diet and Egg Size
Increasing the hen’s intake of balanced protein will result in an increase in egg size while feeding higher levels of protein at the onset of production may help to increase egg size more rapidly. For strains of birds that produce many extra large eggs during the latter part of their egg production cycle, lowering the level of dietary protein during this period will result in slightly smaller and more uniform eggs.
In these situations, when considering changes to the level of dietary protein, the energy content of the diet must also be taken into account. If diets are suboptimal in energy, little increase in egg size will be noted by increasing the level of protein since the hen will utilize protein to meet requirements for energy. Indeed, one of the main factors limiting early egg size is that energy intake is suboptimal in many flocks that come into production at a young age and rise to peak production very rapidly. Where responses in egg size have been noted by adding tallow to laying diets, the rations (in most cases) have been low in energy and the increased energy has resulted in less protein being utilized for energy purposes. The effects of protein and energy on egg size are clearly demonstrated in Figure 11, which depicts the bird’s response to a range of nutrient intakes. Unlike the situation with egg production (Figure 1), there is an obvious relationship between increased egg size and increased protein intake. At low protein intakes (less than 14-15 g/d), there is an indication of reduced egg size when energy intake is increased.
While it is fairly well established that levels of dietary crude protein and certain amino acids will influence egg size, it is not always clear if the responses recorded to crude protein per se can be totally attributed to intake of component amino acids. Table 11 shows a summary of six experiments reported by Waldroup where a range of methionine levels was tested at 0.2% cystine for various ages of bird. Table 11 indicates that as methionine level of the diet is increased, there is an almost linear increase in egg size. As the bird progresses through a production cycle, the egg weight response to methionine changes slightly. In the first period, between 25-32 weeks, using 0.38 vs 0.23% methionine results in a 5.6% increase in egg size. Comparable calculations for the other age periods show 7.3% improvement from 38 – 44 weeks, and 6.7% and 6.0% at 51- 58 and 64-71 weeks respectively. The egg weight response to methionine therefore, closely follows the normal daily egg mass output of the laying hen. In another recent study, Jensen shows a generalized curvilinear response in egg weight to graded levels of methionine (Figure 11).
Over the last few years, there has been considerable research involving the source of methionine as it affects layer performance. When comparing DL-methionine with Alimet, Harms shows the classical response of egg weight to both methionine sources (Table 12).
There has been a suggestion that L-methionine may in fact be superior to any other source. This product is not usually produced commercially because routine manufacture of methionine produces a mixture of D- and L-methionine. This is the only amino acid where there is apparently 100% efficacy of the D-isomer. However, most research data indicates no difference in potency of L- vs DL-methionine sources.
Attempts at reducing or tempering egg size later in the production cycle by phase feeding of protein or methionine have met with only limited success, likely due to the fact that producers are reluctant to use very low protein diets. Our studies indicate that protein levels around 13% and less are necessary to bring about a meaningful reduction in egg size (Table 13). However with protein levels much less than this, loss in egg numbers often occurs.
Methionine levels can also be adjusted in an attempt to control late cycle egg size. Results of Peterson show the tempering of egg size with reduced methionine levels (Table 14). However, these results are often difficult to achieve under commercial conditions because reduction in diet methionine levels often leads to loss in egg numbers and body weight. Phase feeding of amino acids must, therefore, be monitored very closely. As stated at the outset of this section, mature body weight is the main determinant of egg size, and this applies particularly to late-cycle performance.
The best way to control late cycle egg size is through manipulation of body-weight at time of light stimulation. Larger birds at maturity will produce much larger late cycle eggs and vice versa. There is an obvious balance necessary between trying to reduce late cycle egg size without unduly reducing early cycle egg size. Waldroup recently outlined estimates of methionine and methionine + cystine requirements for both egg production and for egg weight/mass (Table 15).
During peak egg mass output (38-45 weeks), the methionine requirement for egg size is greater than for egg numbers, while the latter requirement peaks at 51-58 weeks of age. If these data are verified in subsequent studies, it suggests that we should be very careful at reducing methionine levels much before 60 weeks of age.
It is well known that linoleic acid also affects egg size. Although there is some controversy as to the level required for maximum egg size, it would appear that a level of 1% in the diet should be adequate. Results from a trial aimed at increasing early egg size with high levels of linoleic acid are shown in Table 16. In this study, linoleic acid had no effect on egg size. It should be pointed out that this particular flock matured early and peaked very rapidly. It might well be that the pullets were producing maximum egg mass with respect to body size and thus could not use additional nutrients to advantage.
"Pickouts and Blowouts"
In the past, pickout or blowout losses of 2 to 3% per month over several months after housing pullets were not uncommon. Such losses were usually the result of a number of factors working together rather than any single problem. In most cases, the problem was due to picking rather than any physical stress resulting in "blowouts". Some of the problems that can lead to pickouts or blowouts are as follows:
- lights too bright (or sunlight streaming into buildings)
- pen temperature too high (poor ventilation)
- improper beak trimming - pullets carrying an excess of body fat
- poor feathering at time of housing
- too early a light stimulation
- too high protein/amino acid in the diet causing early large egg size relation to body and frame size
The condition is usually accentuated in multiple bird cages and is a factor of floor space per bird rather than bird density. Frequently, the incidence of picking has been shown to be higher in multiple bird cages where there is in excess of 460 sq cm of space per bird. When birds are more crowded, they do not seem to be as aggressive. One of the most effective ways of avoiding a problem is to keep the light intensity low. Where rheostats are available, these should be adjusted to a sufficiently low level that picking or cannibalism is kept to a minimum. With early maturing pullets, or pullets that reach peak production two to three weeks earlier than was commonly found a few years ago, a mortality picture similar to those outlined above, is seldom encountered. However, what many producers are encountering is a pickout problem that starts around peak production and, although not high, (less than 0.5% per month) often remains with the flock throughout the entire laying period. While this type of problem is aggravated by bright lights, as well as crowding and poor beak trimming, it is felt that one of the main factors triggering the condition is low body weight. Even if pullets mature at body weights recommended by the breeder, many of them are up to 100g lighter than standard at peak production. This, we suspect, is due to the fact that the pullet is coming into production with a minimum of body reserves; it also has a low feed consumption as it has been conditioned on a feed intake near to maintenance just prior to commencement of lay and thus has not been encouraged to develop a large appetite. The pullet is laying at a rapid rate and thus utilizes her body reserves (fat) in order to maintain egg mass production. This smaller body weight bird is often more nervous and so more prone to picking. Under these conditions, the nutritional management program of pullets outlined earlier in this chapter should be followed.
Prolapse can sometimes be made worse by feeding high protein/amino acid diets to small weight pullets in an attempt to increase early egg size. Coupled with an aggressive step up lighting program, this often leads to more double yolk eggs and so greater incidence of prolapse and blowouts. Such pullets are often below standard weight at 12-14 weeks, and so any catch-up growth is largely as fat, which also accentuates the problem. Being underweight at 12-14 weeks usually means that they have reduced shank length, and because the long bones stop growing at this time, short shanks are often used as a diagnostic tool with prolapse problems in 22-24 weeks old pullets.Layers