Maternal flaxseed diet did not affect body weight of broiler chickens diagnosed with novel avian reovirus and infectious bronchitis

DESCRIPTION OF PROBLEM

Omega-3 fatty acid (n-3 FA) enriched maternal diets can potentially improve offspring health. In humans, n-3 FA necessitates immune function maintenance, including mediating inflammatory responses and anti- and pro-inflammatory eicosanoid regulation (Schmitz and Ecker, 2008). The benefits of n-3 FA on immune functions can also be seen in chickens. Chicks that hatch from eggs deficient in n-3 FA can be underdeveloped, resulting in compromised immune health (Cherian, 2015). Chicken adaptive immune response develops at around 2 wk of age; therefore, passive immunity acquired from the mother in the egg is vital (Smith et al., 1994).

All chickens, but especially commercially housed chickens, are at risk of illnesses, including respiratory and enteric diseases (Jones et al., 2019). Feeding poultry breeders n-3 FA has enhanced passive immunity and response to vaccination in progeny (Thanabalan and Kiarie, 2021). For example, supplementing egg-laying chicken breeders with flaxseed increased antibody titer production of their offspring when vaccinated against Newcastle disease and infectious bronchitis (Akbari Moghaddam Kakhki et al., 2021).

Avian reovirus can be transmitted horizontally between and within groups of chickens and vertically from parent stock to offspring via the egg. Avian reovirus infection can result in various clinical diseases, including viral arthritis, runting and stunting syndrome, malabsorption syndrome, chronic respiratory disease, and immunosuppression. Symptoms include poor feathering, growth stunting, a high percentage of runts in a flock, and poor feed conversion (Jones, 2013). Infectious bronchitis is a highly contagious upper respiratory tract infection that transmits horizontally. Infectious bronchitis can result in coughing, sneezing, facial swelling, and reduced weight gain (Jackwood and de Wit, 2013). Both conditions in broiler chickens would decrease growth performance.

The broiler chickens in this report were part of a larger research project assessing the effects of maternal fed n-3 FA on the cognition and fearfulness of their offspring (Whittle, 2023). This report presents body weight, uniformity, feed intake, and feed conversion ratio data for broiler chickens from breeder hens fed a flaxseed or control diet in the rearing and laying period. In this case study, broiler chickens experienced a natural, unexpected disease outbreak of Infectious Bronchitis and Avian Reovirus.

MATERIALS AND METHODS

Medical History

Cohort 1 was diagnosed with Delmarva Bronchitis at 2 wk of age, and Cohort 2 began to show symptoms of bronchitis at 5 d of age (sneezing, coughing). All birds were administered tetracycline hydrochloride (Onycin 250 – Vetoquinol N.-A. Inc., 2000, ch. Georges, Lavaltrie, QC, Canada J5T 3S5) for 5 d in drinking water. The medication was administered using an automatic proportioner using 15 mL of stock solution (400g onycin 250 in 7.5l of water) per 4L of drinking water. Approximately 10% of broiler offspring had feather deformities (curled feathers or helicopter wings) or retained downy feathers until processing age (Figures 1A and 1B). Birds were severely stunted (Figure 1C). Feather deformities and “stunting and runting” are both indicative of avian reovirus infections. The weight range of broilers at 6 wk of age was 699 to 2,357 g. Postmortem analyses showed ingestion of litter, pale shanks, large bursa, and excess mucus in the trachea indicative of malabsorption syndrome and associated with avian reovirus.

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Figure 1. Broiler chickens during disease outbreak of infectious bronchitis and novel avian reovirus. Image (A) and (B) show broiler chickens with wing feather abnormalities, with image (A) also showing downy yellow feathers remaining on the back at 5 wk of age. Image (C) compares 2 broiler chickens at 4 wk of age with the blue-marked chick being runted, whereas the pink-marked chick was also stunted (∼2/3 of target weight).

Blood samples were collected by a veterinarian at 35 d of age intravenously from 10 random individuals. They were analyzed at the Animal Health Laboratory, University of Guelph. Blood serum was extracted, and ELISA tests were used to test for avian reovirus and infectious bronchitis titer presence. The blood analysis tested negative for avian reovirus but positive for infectious bronchitis. Overall, conclusions were that symptoms pointed to a vertically transmitted novel reovirus strain that was not detectable with the ELISA test. Other cases were also reported regionally in broiler chickens of the same strain.

Statistical Analysis

Linear mixed-effects models were used in R v4.1.2 and R Studio using the “lme4” and “emmeans” packages to analyze body weight and uniformity (CV%). Uniformity was calculated as the coefficient of variation (%) = (standard deviation/mean) * 100. Body weight data were log-transformed to increase model fit. Graphs show raw data (Figure 2). Breeder hen rearing diet, laying diet, offspring sex and week of age were used as fixed effects. Broiler offspring pen was used as the experimental unit. Broiler individual nested in offspring pen was used as a random effect for weight data, and offspring pen was used as a random effect for offspring uniformity. Repeated measures were accounted for in the random effects. Significant pairwise comparisons were analyzed using pairwise Tukey tests adjusted for multiple testing. Feed intake and feed conversion ratio were analyzed using analysis of variance using a Tukey test to explore pairwise comparisons from the “stats” package.

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Figure 2. (A) Average weight of broiler chickens from broiler breeders fed with or without flaxseed during laying period compared with the averaged male and female Ross 708 target weights (red solid line) (Aviagen, 2022). All treatments groups were diagnosed with infectious bronchitis and novel avian reovirus during an unexpected disease outbreak. Different breeder diets are shown as control (gray line) and flaxseed (black line). (B) The interaction between age and sex (P < 0.001, males: dotted line, females: solid line). Differences between diets (A) and sexes (B) at each age are indicated as: 0.05 < P < 0.1 = “˙”, P < 0.05 = “*”, P < 0.01 = “**”, P < 0.001 = “***”.

RESULTS AND DISCUSSION

The broiler chickens in the current study consistently weighed less than the average male and female target weight for Ross 708 broiler chickens due to the unexpected outbreak of avian reovirus and infectious bronchitis at the research facility (Figure 2A) (Aviagen, 2022). Week of age significantly interacted with maternal rearing diet (χ² = 18.61, P = 0.002), maternal laying diet (χ² = 40.69, P < 0.001), and sex (χ² = 11.86, P < 0.001). Broiler chicks from the hens fed flaxseed diet in the laying period weighed less than those from control-fed mothers at 6 wk of age (z = 2.84, P = 0.005, flaxseed 1,614.4 ± 21.2 g, control 1,669.7 ± 20.6 g). They tended to weigh less at 5 wk of age (z = 1.70, P = 0.09, flaxseed 1,131.9 ± 9.7 g, control 1,192.1 ± 10.0 g) (Figure 2A). There were no other significant pairwise comparisons within week of age (P > 0.24). There were no significant pairwise comparisons for the interaction between rearing diet and week of age (P > 0.16). Pairwise comparisons between weeks of age were not considered due to a lack of biological relevance. Interestingly, female broiler chickens weighed more than male broiler chickens until 6 wk of age (Figure 2B). This result is surprising; usually, male broiler chickens weigh more than females (Aviagen, 2022). One explanation is that the immune challenge affected (stunted) male broilers differently than females. While literature comparing male and female offspring is scarce, Bowling et al. (2018) found sex-dependent effects of feed restriction of broiler breeder hens on both the growth and immune response of their chicks, with male chicks having poorer growth and female chicks having better immune response when broiler breeder hens were feed restricted.

Overall, CV% got worse with age (χ² = 183.51, P < 0.001). The average CV% ± SE averaged across all treatment groups for each age are: 1 wk 11.9 ± 0.42, 2 wk 15.3 ± 0.55, 3 wk 16.4 ± 0.46, 4 wk 17.8 ± 0.47, 5 wk 18.2 ± 0.47, and 6 wk 18.3 ± 0.66. There was no effect of the maternal rearing diet (χ² = 0.21, P = 0.65), maternal laying diet (χ² = 0.00, P = 0.99), nor the interaction between them (χ² = 0.61, P = 0.43) on the CV% of broiler offspring. The CV% ± SE averaged across week of age for each maternal diet combination is: control–control 16.2 ± 0.54, flaxseed–control 17.0 ± 0.44, control–flaxseed 16.8 ± 0.44, and flaxseed–flaxseed 16.3 ± 0.50. In terms of uniformity, a flock affected by disease may have decreased uniformity compared to healthy flocks. Based on previous literature suggesting that maternal flaxseed diets increase the immune competence of offspring (see review by Thanabalan and Kiarie, 2021), we would have expected control-control groups to have the poorest growth performance. However, we found similar uniformity between broilers from different maternal diet treatments, suggesting that maternal feeding of n-3 FA diets did not benefit their offspring during a disease outbreak.

Feed intake and FCR data are not shown in figures or tables. There tended to be an effect of maternal rearing diet on cumulative feed intake of 6-wk-old broilers (F = 3.35, P = 0.07). Broilers from mothers fed flaxseed in the rearing period had a higher cumulative feed intake (2,703 ± 41.2 g/bird) than those from mothers fed control diets during rearing (2,639 ± 35.6 g/bird). The laying diet had no effect (F = 0.65, P = 0.42) nor the interaction between maternal rearing and laying diet (F = 2.34, P = 0.13) on offspring feed intake. The cumulative feed intake (g/bird) for each maternal rearing-laying diet combination for 6-wk-old broilers is as follows: control–control 2,622 ± 31.0, flaxseed–control 2,639 ± 48.5, control–flaxseed 2,582 ± 63.6, and flaxseed–flaxseed 2,767 ± 61.2. The cumulative feed intake of 6-wk-old broilers was projected to be 4,324 g (Aviagen, 2022). In this study, broiler offspring did not consume as much feed as expected. Decreased appetite is associated with sickness behavior (Linares et al., 2018). Therefore, it was unsurprising that feed intake of immune-challenged broilers was less than that expected for healthy broilers.

Maternal rearing (F = 4.54, P = 0.04), laying diet (F = 6.23, P = 0.02), and their interaction (F = 3.7, P = 0.06, tendency) effected broiler FCR. The FCR for each maternal rearing-laying diet combination is as follows: control–control 1.65 ± 0.03^a, flaxseed–control 1.66 ± 0.04^a, control–flaxseed 1.66 ± 0.05^a, and flaxseed–flaxseed 1.86 ± 0.05^b. Significant pairwise comparisons (P < 0.03) between maternal rearing-laying diet combinations are indicated by different superscript letters. This result suggests that broilers from mothers fed flaxseed during the rearing and laying period were the least efficient; they consumed more feed and weighed less than other treatment groups. The feed conversion ratio for 6-wk-old broilers should be 1.51 (Aviagen, 2022). All treatment groups in this study grew slower, ate less, and grew less efficiently than expected of healthy broilers.

We found no evidence that a maternal flaxseed diet provided an advantage to broiler chickens under a naturally occurring immune challenge. We observed the contrary, with offspring from mothers fed flaxseed weighing less, eating more, and having a poorer feed conversion ratio. It is important to note that there is some contrary evidence in the literature to suggest that n-3 FA supplemented diets can have negative or immunosuppressant effects, including decreasing the immune response to viral and bacterial infections (Al-Khalifa et al., 2012). An additional factor can be the source of n-3 FA, as marine sources (i.e., fish oil and algae) are higher in EPA/DHA, with different biological properties than plant sources (i.e., flax). While evidence suggests that maternal-fed n-3 FA from flaxseed increased antibody titer production in response to an infectious bronchitis vaccine in layer chicks (Akbari Moghaddam Kakhki et al., 2021), and increased passive immunity transfer from broiler breeder hen to their chicks (Wang et al., 2004), it is difficult to speculate how this may translate to a natural disease challenge.