Poultry meat is one of the most important protein sources in human diet and production is worldwide growing. Global poultry meat production in 2000 was 69 million tons and this increased to over 97 million tons in 2010 (Windhorst, 2011). This equates to an annual production of approximately 70 billion broilers originating from approximately 600 million broiler breeders. So a relatively small number of broiler breeders has a major impact on the poultry meat chain and optimizing management of breeders will have benefits for the total chain. Broiler breeders need to produce first class and healthy chicks (Zuidhof et al., 2007). Due to the continuing increase in the genetic potential of the offspring (e.g., Havenstein et al., 2003a,b; Renema et al., 2007b; Zuidhof et al., 2014) this is becoming increasingly challenging. In the past, obesity, mainly in the second phase of the laying period, was a major problem in broiler breeder flocks and resulted often in a decreased reproduction rate during the laying period (Bornstein et al., 1984; Leclercq et al., 1985; Cahanar et al., 1986; Robinson et al., 1993). Overweight hens have sperm storage problems (due to the fat deposition in the sperm storage glands) and physical problems during the cloacal contact during natural mating (Mc Daniel et al., 1981). The body composition of breeders, however, has changed dramatically during the last five to six decades (Havenstein et al., 2003a; de Beer, 2009). In modern broiler breeders, obesity is not an issue anymore, due to the selection of strains with increased breast muscle and decreased fat pad deposition characteristics (Havenstein et al., 2003a). The selection for increased feed efficiency, growth rate and body fat content has not only affected the offspring but also the parent stock. This was recently confirmed by Eitan et al. (2014) who compared a 1980 to a 2000 breeder strain. The 2000 strain contained 42% more breast meat (21.2 vs. 14.9% of BW) and 50% smaller abdominal fat pad (2.7 vs. 5.4% of BW) compared to the 1980 strain. A key issue in broiler breeder production is the decrease in fertility and hatchability of eggs, especially in the second part of the laying period. Fertility of hatching eggs declined from 88.8% in 2000 to 84.7% in 2005 (van Emous, 2010). This decrease in fertility may be caused by a wide range of factors such as strain, health status of the flock, egg size, egg weight, egg quality, egg storage duration and conditions, egg sanitation, season of the year, and age of the breeders (as reviewed by Yassin et al., 2008). Besides these factors, nutrition played a very important role on fertility and hatchability. A negative effect of a high daily crude protein intake (> 25 g/d) during the laying period on fertility or hatchability of eggs has been reported by Pearson and Herron (1982), Whitehead et al. (1985) and Lopez and Leeson (1995a). A decreased hatchability of fertile eggs could be explained by an increased embryonic mortality as shown by Pearson and Herron (1982) and Whitehead et al. (1985). Ekmay et al. (2013) showed that increasing levels of dietary lysine and isoleucine at peak production results in a reduction in fertility. An explanation for this effect on fertility was postulated by de Beer (2009), who suggested that an increase in CP intake leads to an increase in nitrogen excretion (de Beer, 2009; Lopez and Leeson, 1995a). This excessive nitrogen excretion may lead to an alkaline environment near the cloaca, where the sperm host tubules are located, with detrimental effects on the semen quality stored in these tubules. Feeding high yield breeders high levels of amino acids (e.g. lysine) will also lead to more muscle production and this extra muscle requires more energy to maintain (de Beer, 2009). Therefore, during the last decade several researchers have reported that broiler breeders need a certain proportion of body fat at the onset of lay for subsequent reproductive performance (Sun and Coon, 2005; de Beer, 2009; Mba et al., 2010). Because tissue growth is directly affected by dietary nutrient composition, a nutritional approach to this topic was highly relevant. Therefore, the overall practical objective of the present study was to develop new feeding strategies during the rearing and laying period for broiler breeders in order to alter body composition with positive effects on reproduction, offspring and welfare, for a more sustainable approach of broiler breeder production. Therefore the overall objective of the present presentation is to give an overview of the effects of nutrition of breeders during the laying period on reproduction performance.
Effects of protein intake during lay on breeder performance
The different feeding strategies during the laying period as described by van Emous et al. (2015a) did not affect breeder performance in the second phase, however, the high and low energy diet during the first phase resulted in a slightly lower number of eggs. It is not really clear what caused the difference in egg production during this laying phase. It was observed that a high energy diet resulted in a decreased feed intake and decreased eating time (van Emous et al. 2015c). The most aggressive breeders ate a larger amount of feed resulting in decreased flock uniformity (Renema et al., 2013). A less uniform flock will reach peak production somewhat later caused by the larger variation in sexual development of individual birds (Laughlin, 2009). However uniformity during initial lay was not recorded in the study of van Emous et al. (2015a), the more than 5 d delayed peak egg production for the birds fed the high energy diet is an indication of a decreased uniformity. It could also be hypothesized that a low energy diet (and thus high daily protein intake) resulted in more breast muscle deposition. This might increase the daily energy requirement for maintenance and decreases, therefore, the amount of energy that remains for egg production (Ekmay et al., 2013). In general, egg weight is affected by daily dietary protein and amino acids intake (Lopez and Leeson, 1995a; Fisher, 1998; Joseph et al., 2000). More specific, a higher egg weight is caused by a higher daily intake of sulphur amino acids (effect on albumen and yolk) and/or higher daily intake of linoleic acid (effect on yolk). This was confirmed in the study of van Emous et al. (2015a) in the second phase of the laying period when daily amino acids and linoleic acid were increased. In the first phase of lay, the higher daily intake of amino acids was compensated by the lower daily linoleic acid intake potentially resulting in similar egg weights during that phase. Total mortality during the entire laying period was increased when breeders were fed the high (9.4%) compared to the standard (6.5%) and low (5.7%) energy diets during the first phase of lay (van Emous et al., 2015a). The majority (on average, 67% of the different treatments) of the total mortality was due to ruptures of the gastrocnemius tendons. It was hypothesised by van Emous (2015) that the potential factors below are likely to account for inducing ruptures of the tendons: 1. A lower daily feed intake resulting in a lower daily macro- and micronutrients intake. No literature is available, however, regarding the effect of a lower nutrient intake on tendon development during rearing. 2. Lowering the daily amount of feed decreased time spent on feeding behavior (van Emous et al., 2015c). It was observed that these birds were aggressive at feeding time resulting in (hyper)activity like running and jumping, inducing a higher risk of damaging the tendons. 3. Providing less feed leads to more competition at feeding time and a possible decrease in flock uniformity (unfortunately not recorded) during initial lay. More aggressive birds will develop higher BW due to the higher feed intake with possible effects on the tendon. A combination of factor 2 and 3 seems to be the most reasonable explanation of the differences in mortality caused by ruptures of the tendons.
Effects of protein intake during lay on incubation traits
Feeding a low dietary energy level, resulting in a higher daily protein intake, during the first as well the second phase of the laying period did not affect fertility (van Emous et al., 2015a), which is also found by other authors (Whitehead et al., 1985; Mejia et al., 2012b). In other studies, feeding broiler breeders a high daily protein level during the laying period resulted in decreased fertility (Lopez and Leeson, 1995a; Ekmay et al., 2013). It is not clear what caused the differences between the cited studies but probably causative factors are housing system, diet, and breed. E.g., birds were individually housed and artificially inseminated (Mejia et al., 2012b; Ekmay et al., 2013) or group housed with natural mating (Whitehead et al., 1985; Lopez and Leeson, 1995a; van Emous et al., 2015a). Besides the different ways of housing birds, also different dietary treatments were used for changing dietary protein or amino acids levels. For example, in the study of Lopez and Leeson (1995a) birds received different dietary crude protein levels while essential amino acids levels were equal. Some researchers used semipurified diets (Mejia et al., 2012a,b; Ekmay et al., 2013) and changed specific amino acids levels while other researchers used more practical diets with reduced levels of crude protein or amino acids (Whitehead et al., 1985; van Emous et al., 2015a). In the studies of Pearson and Herron (1982) and Whitehead et al. (1985), older Ross strains were used, while in the study of van Emous et al. (2015a) Ross 308 birds were used. In the studies of Mejia et al. (2012a,b) and Ekmay et al. (2013) Cobb 500 breeders were used while Lopez and Leeson (1995a) used Hubbard breeders. The results from van Emous et al. (2015) showed conclusively that feeding birds a high energy diet (less daily protein intake) during the second phase of lay improved hatchability of fertilized eggs. These results are in agreement with Pearson and Herron (1982), Whitehead et al. (1985) and Lopez and Leeson (1995a). The differences in hatchability of the fertile eggs were caused by differences in embryonic mortality. A higher or lower embryonic mortality leads to a lower or higher hatchability of fertile eggs, respectively. This observation supports the earlier work of Pearson and Herron (1982) who found that lowering daily protein intake (27.0 vs. 21.3 g/bird) resulted in a decreased mortality and malformation of embryos. The decreased embryonic mortality in birds fed the high energy diet (low daily protein intake) in the study of van Emous et al. (2015) can be explained by the lower egg weight (68.7 vs. 69.1 g). Larger eggs have a higher eggshell conductance (EC) due to an increased pore density or pore size (Shafey, 2002). A higher EC increased vital gas exchange and water loss which causes, respectively, an increased early and late embryonic mortality (Peebles et al., 1987). The effect of an improved hatchability and decreased embryonic mortality, while feeding the high energy diet (low daily protein intake), was underlined by the decreased proportion of second grade chicks in the study of van Emous et al. (2015a). The relationship between low embryonic mortality and less second grade chicks was previously found in studies of Reijrink et al. (2010) and Molenaar et al. (2011).
Effects of protein intake during lay on reproduction
Recently a study with a 2 × 2 factorial arrangement was conducted to determine the effects of 2 dietary crude protein levels, high (CPh) or low (CPl), supplemented with free amino acids (AA), and 2 ages at photo stimulation (PS) - early (21 wk; PSe) or late (23 wk; PSl) - on reproduction traits of broiler breeders and progeny performance (san Emous et al. 2018). Diets were isocaloric, and calculated CP content of the CPl diets was 15 g/kg lower than the CPh diets during all phases. Total egg production was similar between CPl and CPh birds during phase 1 and 2 (22 to 46 wk of age) but was reduced by 2.8 eggs for CPl birds during phase 3. For the overall laying period, CPl birds tended (P = 0.075) to produce 4.7 fewer total eggs. Hatchability of set eggs was similar between CPl and CPh birds during phases 1 and 2 but tended (P = 0.064) to be lower for CPl birds in phase 3. PSe birds showed an advanced age at sexual maturity and age at peak production of 4.6 and 5.3 d, respectively, resulting in 2.5 more total eggs during phase 1. During phase 1, PSe birds showed an almost 5% increased fertility. Chick production in phase 1 was higher for PSe birds resulting in a tendency (P = 0.071) to higher overall chick production of almost 8 chicks. Progeny from early PS breeders showed an overall significant lower feed conversion ratio (FCR). It was concluded that egg and chick production during phases 1 and 2 were not affected by dietary CP level, but egg and chick production was reduced for CPl birds during phase 3. On the other hand, PSe birds showed an increased number of chicks.
Effects of protein intake during lay on offspring performance
Relatively few papers are available on the effects of specific protein or amino acids intake of broiler breeders on offspring performance and processing yields (Wilson and Harms, 1984; Lopez and Leeson, 1995b; Mejia et al., 2013). In general, little or no effect of a change in maternal daily protein intake on growth and processing yields of the offspring has been reported. This is in agreement with the results of the two broiler trials obtained of hatching eggs from 28 and 53 wk of age during the study of van Emous (2015). Breeders fed similar amounts of daily energy, but 7% more or less protein during the first phase of the laying period showed no difference in performance and processing yields of offspring from 28 wk old breeders. Moreover, feeding breeders a 9% lower daily protein intake during the second phase of the laying period did not, except a decreased mortality, affect broiler performance and processing yields of offspring from 53 wk old breeders as well. The lack of an effect of daily protein intake on offspring performance and processing yields can be explained by the research of Ekmay et al. (2011). They found that 60 to 70% of egg albumen lysine is derived from skeletal muscle reserves and the remainder from dietary resources. They suggested that skeletal muscles probably functioned as a transient protein pool from which lysine can be mobilized.
Separated sex feeding
Separate male and female target weight curves are given for many years in breeding company management guides. Worldwide in the broiler industry, males are typically reared separately from the females so that growth and development can be controlled (Fisher and Gous. 2009). The techniques for feeding the sexes separately after mixing were introduced by McDaniel (1986). This underlying concept could be stated quite simply as ‘It is beneficial to provide feed separately to males and females in order that the physical amounts and potentially feed type can be varied between the sexes (Laughlin, 2009). This allows separate control of male body weight during the production period and female feed amount to ensure continued production.’ Since that time there has been extensive work on the precise nature of the control and the methods to effect it. Essentially a system was developed in which the females were provided with feed in feeders from which the males were physically excluded and the males were fed in feeders which were positioned at a height which the smaller females could not access. Differences in relative heights and head sizes of males and females, age at mating and feeder types have led to much practical refinement of the original concept. Such a system offered the possibility to provide a separate feed type to the males and females. A relative old experiment shows that using different separated sex feeding during the laying period results in a better-controlled body weight of the males and as a consequence an improved fertility in the last part of the laying period (Stappers and Vahl, 1991). It has been estimated that mating frequency is 5 to 10 times higher in a broiler breeder house as compared to flocks of chickens housed under natural conditions (van Emous, 2010). This relatively high frequency of mating may affect the relationship between males and females, resulting in females avoiding males as hypothesized by Fontana et al. (1992). Over-mating might be avoided by separating females and males temporarily during the day. Based on this hypothesis, a new housing system for broiler breeders, called the Quality Time® Concept (QTC), has been developed (van Emous, 2010). Males are separated from females during 5 hours per day, using a separate feeding system and a moving fence. After a successful pilot experiment, two on-farm experiments were carried out in a broiler breeder house with 15,000 birds. The house was divided in six compartments. In the QTC compartments more voluntary and successful matings were observed. Also, quality of the sexual behavior improved which resulted in an improved feather cover between 37 and 48 weeks of age in the QTC compartments as compared to the control compartments. Separating males from females did not increase aggressive behavior between the males in the male pen (van Emous, 2010). In the first flock, no effect on fertility was found, however, in the second flock fertility was improved with 1.5%.
Specific male diets
The use of separate feeds for males is a very variable practice, and the feeding of males on the same feed as the females is probably most widespread (Fisher and Gous, 2009). Thus males frequently receive far more nutrients than required, especially calcium and protein, and the most important question is whether this is detrimental to biological performance. The rearing of males and the assessment of their lifetime performance are even more difficult than for females, and hence nutritional effects remain very uncertain. Overall there does seem to be a negative effect of higher protein levels, in growth at the later stages of rearing and during the reproductive period, but it is not well quantified. A recent publication by Romero-Sanchez et al. (2007) describes a well-executed trial and also illustrates very well the difficulties involved. These authors reared males from 2 to 26 weeks of age on two growth patterns, described as ‘concave’ and ‘sigmoid’, using rearing feeds with 140 or 170 g/kg crude protein. However, it is clear that the higher level of protein depressed fertility, especially in combination with the concave feeding program, which involved a higher level of feeding in the later stages of growth. In early studies of the effect of dietary protein in the feed given during the breeding period, McDaniel (1986) demonstrated that male fertility is improved when low-protein feeds are used, and this led to the practice of separate-sex feeding of breeders. Subsequently, several papers have investigated the effect of crude protein (CP) on semen production and fertility in broiler breeder males (Wilson et al., 1987a,b; Hocking, 1989; Hocking and Bernard, 1997; Zhang et al., 1999). Although the effects are not universal, the general conclusion from this research corroborates the work of McDaniel (1986), showing that low-CP diets have an advantage in semen production over high-CP diets.
Presented at AMEVEA Nutrition Seminary, Bogotá, Colombia. November 2018.