Precision feeding of broiler breeders

Modern broilers grow 5 times faster on 40% less feed than they did 60 years ago (Zuidhof et al., 2014). Because high body weight (BW) correlates negatively with reproduction and health (Decuypere et al., 2010), the severity of broiler breeder feed restriction increases every year relative to broiler growth potential. This intensifies competition for feed, resulting in unequal distribution of feed and poor flock uniformity. Achieving and maintaining high flock uniformity is one of the biggest management challenges for contemporary hatching egg producers. A precision feeding (PF) system was developed at the Poultry Research Centre at the University of Alberta to solve this issue. The PF system allocates feed to individual floor housed birds after comparing each individual’s BW to a recommended target BW. The system automates complex feed allocation decisions, freeing the flock manager to focus on higher level decisions. The PF system can now consistently achieve 1% coefficient of variation (CV) in BW at photostimulation age, so we can now refine our questions to include, “What is the right target BW for broiler breeders?” “How much should we feed broiler breeders, and when?” and “What optimal dietary nutrient concentrations optimize a broiler breeder’s entry into lay, and subsequent reproductive performance?” The PF system requires a radical change to the traditional thinking that is second nature for those experienced in feeding birds once per day as one big group. Precision feeding has been challenging the way we think about nutrition, reproductive physiology, and behaviour in broiler breeders. The big data collected by the system provides analytical opportunities we have never had before. This has evolved our thinking, and has led to new insights around broiler breeder metabolism, physiology, productivity, and behaviour. Precision feeding has also yielded some unexpected results, which are always an excellent opportunity to develop new hypotheses. The goal of this paper is to explore some of the interesting and important new discoveries the PF system has begun to yield.

The observations reported subsequently in this stem from several completed precision feeding studies. A brief description is provided here to help the reader understand both the experiments that will be discussed, followed by a description of how the precision feeding system worked.

Two studies were conducted as direct comparisons of conventional and precision feeding. In the first of these comparison studies, a commercial broiler breeder was used (Ross 308); in the second, a Cobb grandparent (GP) line was used (L35; male line female). Conventional feeding treatments used skip-a-day or daily feeding, and feed allocations were based on weekly BW measurements.

A third study was conducted to evaluate the impact of metabolizable energy (ME) intake on the onset of lay. In this third study, precision fed Ross 308 broiler breeders were divided into two treatments: 1) a standard commercial diet (11.9 MJ/kg) fed to achieve the breeder-recommended target BW, or a high ME diet (13.2 MJ/kg) provided ad libitum.

Two studies evaluated the interacting effects of BW and light management (rearing day length and photostimulation age) on the reproductive efficiency of Ross 708 pullets. The precision feeding system is a sequential feeding system. Instead of all birds eating simultaneously, birds eat any time of the day, one after another. Therefore, we have been exploring questions related to whether we can provide light to stimulate the retina without stimulating the reproductive axis. This would allow us (and eventually commercial users) to increase the time birds can access the feeding system, and decrease capital costs. In both studies, breeder-recommended target BW profiles were contrasted with a higher target BW designed to achieve the 21 wk BW at 18 wk of age, a 22% increase. The first of these studies evaluated the impact of rearing daylength (8L:16D, 10L:14D, and 12L:12D) on breeder performance. The second study explored whether highly uniform birds on the increased target BW could be photostimulated. Thus, birds on the high and low BW treatments were photostimulated at 18 or 21 wk of age.

A more complete description of the feeding system and its operation is disclosed elsewhere (Zuidhof et al., 2016; Zuidhof et al., 2017). Only a brief description is provided here. The PF station is a sequential feeding system. The main functional area of each feeding station is the feeding chamber. The feeding chamber has an entry door, an exit door with an associated ejector mechanism, radio frequency identification (RFID) reader, scales to weigh the birds and feeder, and a feed access door.

Visits to the station are recorded whenever a bird enters the station, whether or not it is provided access to feed. The user can specify the amount of feed to provide in the feeder, and the duration a bird that is allowed to feed retains access to the feed. This time defines the length of each feeding bout. We typically provide 10 to 25 g of feed, and allow access to the feed for 45 or 60 seconds. Birds are allowed to eat any time of the day or night as long as they meet the criteria for a meal, which normally means their BW was less than the target BW at the time of the visit. If multiple birds entered the station, the target BW is greatly exceeded, and the system ejects the birds from the station without feeding them. Prior to each feeding bout, an auger draws feed from a hopper into the feeder until the desired feed amount is present. At the end of each feeding bout, the weight of the remaining feed is measured and feed intake is calculated. After every visit to the station, the date and time at the start and end of each visit, BW, RFID, and feed intake are recorded as a database record.

Over the last couple of years, we have successfully controlled feed intake according to several criteria, including 1) real-time comparison to a set target BW, 2) maximum daily feed allowances, or 3) pair feeding, where we restricted feed intake proportionally to ad libitum fed birds. We have successfully fed males and females, broiler breeders, broilers, layers, and heritage lines.

With PF, we have been able to consistently achieve a coefficient of variation for pullet BW of 1 to 2% by the time of photostimulation. van der Klein et al. (2017) reported a CV of 0.8 % CV for BW at wk 21. In a direct comparison with conventional feeding, Zuidhof (2017) reported a reduction in BW CV in pullets at the time of photostimulation from 14% to 2% using precision feeding. At 21 wk of age, the precision fed birds in that study weighed 99.0% of the target BW compared to 95.3% in the conventionally fed treatment.

Precision feeding had some unexpected effects on development. Higher feeding frequency with the PF system appears to change the nutrient partitioning priorities of feed restricted broiler breeders. This is likely related to the fact that precision fed birds do not regularly fluctuate between the large positive and negative energy balances that occur daily with conventional feeding practices.

By photostimulation age (23 wk), precision fed Ross 308 breeder pullets were leaner, with more breast muscle (20.1% vs. 19.0% of live BW) and less abdominal fat (1.2% vs. 1.6% of live BW) compared with skip-a-day fed pullets (Carneiro, 2016). In a Cobb GP line, conventionally fed birds had 2.6 g of abdominal fatpad at 16 wk of age, compared with only 1.48 g in birds fed with the PF system (P < 0.05), but no difference was observed at photostimulation. This particular GP line was extremely lean. At the end of lay, the precision fed GP hens had a 10% larger breast muscle (124 g increase, P < 0.05) compared with conventionally fed hens.

Similar results were also observed in the commercial Ross 308 line. At the end of lay (55 wk of age) in the study evaluating the interaction between BW and rearing daylength, standard BW hens had a significantly higher proportional breast weight compared with high BW hens (27.5% vs 25.8%, respectively; P = 0.006), and a lower proportional fatpad weight compared high BW hens (1.5% vs. 2.4%, respectively; P < 0.001). This coincided with a lower egg production in the standard BW hens, but it is not clear whether altered body composition caused the drop in egg production or vice versa (van der Klein et al., 2017). In this study, almost one fifth of the standard BW hens never reached sexual maturity. Those hens that did not begin egg production before wk 55 had a 1.15 times the breast muscle of hens that had laid eggs, and 0.63 times the fatpad of hens that had laid eggs. This suggests that if a threshold body fat content or fat mass is required for the onset of lay, it may not have been achieved by some of these precision fed standard BW birds.

During the rearing period, cumulative FCR of precision fed Cobb GP pullets was 3.2% lower compared with conventionally fed pullets (P < 0.05). From 10 to 23 wk of age, cumulative FCR for Ross 308 broiler breeders in the precision fed pullets was 20% lower compared with skip-a-day fed pullets (4.0 vs. 4.8, respectively, P < 0.05). Precision feeding provided us with a means of evaluating efficiency in individual free run birds. In the study with standard and high BW broiler breeders, cumulative FCR phenotypes from d 16 to wk 21 averaged 3.95 ± 0.165. Cumulative FCR for hens on the high BW treatment was 0.33 higher compared with hens on the Standard BW treatment ( Figure 1, P < 0.001). Improved efficiency in precision fed broiler breeder pullets is presumed to be due to the increased feeding frequency (de Beer et al., 2007). Fed once every 24 or 48 h, the pullets need to store nutrients during the immediate post-prandial period when birds are in a high positive energy balance. Conversely, they must mobilize nutrients after nutrient supply from the gut to the bloodstream is reduced. These processes are not 100% efficient, thus the birds expend energy, which is lost as heat, which manifests as a measurably higher FCR. A similar phenomenon has been observed in daily vs. skip-a-day fed pullets (Zuidhof et al., 2015).

Of course, feed consumed per chick produced is the most important measure of efficiency for broiler breeders. Notably, egg production in the high BW treatment was 57% higher (van der Klein et al., 2017), so the extra cost of feeding to the higher BW would pay back large dividends.

From 10 to 23 wk of age, total heat production of precision fed Ross 308 pullets was 74.5 kJ/kg BW^0.68 less than skip-a-day fed pullets (464 vs. 540 kJ/kg BW^0.68, respectively; P < 0.0001). During the early laying phase (23 to 34 wk of age), after the conventional hens were transitioned to daily feeding, this trend continued. Precision fed hens had a lower total heat production (1252 kJ/d) than conventionally fed hens (1307 kJ/d; P < 0.0001).

In Ross 708 pullets from 16 d to 21 wk of age, average daily ME allocated towards maintenance (energy which was lost as heat) was 425 ± 20 kJ/kg^0.7. The ME requirement for BW gain was 10.2 ± 0.24 kJ/g. Hens on the 8L:16D schedule allocated 10.5 kJ/kg^0.7/d less towards maintenance compared to hens on 12L:12D schedule (P = 0.003), and hens on the 10L:14D schedule were intermediate. This was likely due to increased activity levels with longer photoperiods. Hens on the standard BW allocated 21.9 kJ/kg^0.7/d less toward maintenance (P < 0.001) compared to hens on the high target BW (van der Klein and Zuidhof, 2017). Animals are able to adjust feed intake, energy expenditure or both to maintain BW. Feed intake affects energy expenditure and heat production primarily in two ways: diet induced thermogenesis (NRC, 1981), and through homeostatic self-regulation of metabolic rate, which allows birds to maintain their energy balance (Richards and Proszkowiec-Weglarz, 2007). The precision feeding system has allowed us for the first time to model energy expenditure of individual birds in a group housed setting.

Reproduction in chickens is under the control of the hypothalamic-pituitary-gonadal (HPG) axis which integrates external (photoperiod, seasons) and internal (age, body status) cues to ensure survival of the species via hatch of healthy chicks. This axis involves the combination of stimulatory and inhibitory neuropeptides and hormones which, upon photostimulation, result in the activation of the ovary (Bedecarrats, 2015). In turn, early ovarian follicles release estradiol which prepares the hen’s body for egg production by stimulating the development of the reproductive tract, the synthesis of yolk components by the liver, and by terminating skeletal longitudinal growth in favor of medullary bone for egg shell formation. Thus, optimum reproductive fitness is achieved only if the age, body frame and composition, and photoschedule are coordinated. The process of egg formation is energy demanding for the hen and sufficient reserves need to be achieved. However, it is well documented that broiler breeders, when left unrestricted, tend to become overweight at an early age which results in health problems and poor reproduction (Decuypere et al., 2010; Mench, 2002; Yu et al., 1992). As a result, feed restriction to match target growth curves recommended by primary breeders evolved as standard industry practice to optimize reproductive efficiency. However, our most recent data suggest that continuous increase in broiler growth potential may have increased the optimum weight breeders need to reach at the time of photostimulation and, body composition of breeders is directly linked to their ability to respond to photostimulation. Precision feeding is the only on-farm technology which allows nutritional intervention at the bird level to ensure proper growth and body composition to match breeder hens’ metabolic status, age and photoperiod.

Bedecarrats et al. (2016) hypothesized that in addition to the classically considered sexual development thresholds (age, daylength, BW, and carcass fat content), metabolic status also plays an important role in the onset of lay. Precision fed birds are provided small meals throughout the day, rather than the conventional single large meal. “Just in time” nutrition allows PF birds to access nutrients directly from the gut, and their metabolism appears to shift from fat storage toward preferentially building muscle tissue. This is consistent with the observation that skip-a-day fed pullets retain less breast muscle and more fat compared with conventionally fed pullets fed once per day (Zuidhof et al., 2015). This may explain the unexpected negative impact of PF on egg production when broiler breeders are exactly at the breeder-recommended target BW. Serendipitously, high feeding frequency with PF may have allowed us to see how close current target BW recommendations are to being insufficient for sexual maturation and reproductive success.

In Ross 708 hens, a long (12L:12D) rearing photoschedule caused a delay in the onset of lay. However, this effect and the associated negative impact on total egg production was mitigated by growing birds to a greater BW target (van der Klein et al., 2017). In fact, all hens on the high BW target reached sexual maturity, whereas 38% of standard BW treatment birds on the long rearing photoschedule did not begin laying during the entire trial (to 55 wk of age). This leads us to the hypothesis that a yet-to-be defined metabolic cue may play an important role in the timing of sexual maturation.

When Ross 308 broiler breeders were allowed to consume a lot of energy after photostimulation, they also started to lay earlier compared with the birds on a standard BW trajectory and diet. High ME intake increased the expression of gonadotropin-releasing hormone gene in the hypothalamus and its receptor in the anterior pituitary, which is known to activate the HPG axis leading to sexual maturation and ovularche. By 26 wk of age, only 50% of the standard ME intake birds had ovulated, but 100% of the high ME intake treatment (P < 0.001).

In our first two studies comparing reproductive efficiency in conventional and precision fed hens, we rejected the hypothesis that a highly uniform flock would increase egg production. Egg production in precision fed Ross 308 breeders was only 84% of the conventionally fed birds (P < 0.0001). Egg production in precision fed Cobb GP hens was only 80% of the egg production of conventionally fed breeders (P < 0.001). However, in another study, it became clear that a higher BW target corrected the problem of reduced egg production by PF hens. Precision fed hens on the high BW treatment produced 138 eggs to 55 wk of age, while PF hens on the standard BW treatment produced only 88 eggs (P < 0.001) (van der Klein et al., 2017). These results, together with the decrease in abdominal fatpad, are consistent with the hypothesis that metabolic triggers are also likely involved in sexual maturation. Broiler selection has occurred so rapidly that the primary breeders understandably have not been able to keep up with the development of optimal target BW recommendations for breeder stock. These have changed very little since feed restriction became standard practice (Renema et al., 2007), and may very soon need to be adjusted upward.

In trials with parent and grandparent stock, overall fertility to 52 weeks of age was 91.8%; significantly higher compared with conventionally fed pullets (89.9%; P = 0.002). In Ross 708 breeders, fertility to 55 wk of age was over 95% in both the standard and high target BW treatments, and they were not significantly different from each other. The high levels of fertility may well be attributable to strict control of male BW. Precision fed males are always in a slight positive energy balance because the target BW increases slowly during the laying and mating period. If males are reproductively active, they lose more dietary energy as heat.

However, this metabolic weight loss is replenishable in the PF system. Although these birds would lose weight more quickly, they would also qualify for a meal more quickly, and gain back any lost weight. Conversely, less active males are prevented from becoming overweight because they are weighed every time they attempt to have a meal. In the Ross 708 study, there were several roosters that needed to be replaced even though their BW was very tightly controlled. There were many hatching egg producer concerns about that particular rooster strain as being hard to manage. Notably, in the Cobb GP trial, no spiking was needed in the PF treatment.

Precision feeding is a valuable tool for research in chickens that generates large volumes of information that have allowed our thinking about nutrition, metabolism, and reproduction to evolve. We will use the PF system to investigate additional factors influencing onset of sexual maturity and reproductive fitness in chickens. Our research has raised a warning flag about an impending biological limit to feed restriction, and clearly indicates a need to reevaluate target BW standards. It also points to the importance of identifying metabolic factors that mediate the function of the HPG axis. Because the precision feeding system allows us to collect large amounts of data and control feed intake to minimize BW variation, it serves as an excellent tool to study the interacting effects of diet composition, feed allocation, and other management factors on subsequent changes to body composition and reproductive success at the individual hen level. Even as these fundamental questions are addressed, precision feeding has excellent potential as a management system for commercial broiler breeders and upstream breeding stock.

ACKNOWLEDGEMENTS: Financial support from Alberta Livestock and Meat Agency, Agriculture and Food Council, Ontario Ministry of Agriculture, Food and Rural Affairs, Canadian Poultry Research Council, Alberta Innovates Bio Solutions, Cobb-Vantress, Inc., Alberta Hatching Egg Producers, Canadian Hatching Egg Producers, Danisco (a division of DuPont), Poultry Industry Council, and Alberta Chicken Producers is gratefully acknowledged. Special thanks to in kind support from Mark Fedorak (Xanantec Technologies, Inc.) for in kind support for the feeding stations and Chris Ouellette for outstanding technical support.