Mortality often is much higher in male than in female broiler breeders (36.2 per cent and 11.1 per cent, respectively), making it necessary to introduce additional males during the breeding cycle, according to J.R. Moyle and colleagues at the University of Arkansas, US, in a paper published in International Journal of Poultry Science.

The authors explain that, while it is known that males perform better on low–protein diets, they usually are fed the same diet as the hens in order to reduce feed transportation costs and eliminate the chance of the hens receiving the wrong feed. Breeder hen diets are high in calcium (Ca), which may be detrimental to male performance and may cause kidney damage as the males excrete the excess calcium.

Urolithiasis was defined by Wideman as ‘an acquired degenerative kidney disease of pullets and laying hens involving focal mineralisation of the kidneys, progressive obstruction of the ureters by uroliths (kidney stones) and kidney atrophy ‘upstream’ of the site of ureteral obstruction combined with compensatory hypertrophy by the undamaged portions of the kidney’.

In an effort to understand the extent of kidney damage that occurs in male broiler breeders, 136 males that had been on commercial breeder hen diets for 41 or 42 weeks were euthanised and their kidneys evaluated by the Arkansas group. The diet contained 16 per cent protein, 3.25 per cent calcium, 0.4 per cent non-phytate phosphorus and approximately 2,860kcal per kg.

Data collected included body weight, left and right kidney weights and the incidence of macroscopically visible uroliths within the ureters or ureteral branches. The bilateral symmetry of the two kidneys (heavy:light kidney weight ratio) was assessed as an indicator of subclinical kidney damage.

The results revealed that only 55.6 per cent of the males had kidneys that were bilaterally symmetrical (within 10 per cent by weight). Left kidneys were significantly heavier than right kidneys (10.07 versus 9.26g, respectively) and the left kidney was larger in 76.3 per cent of the birds.

Uroliths were found in 7.4 per cent (10/136) of the males.

Moyle and co-authors concluded their results indicate that broiler breeder males fed high levels of calcium develop kidney asymmetry and urolithiasis, which can contribute to their high mortality levels.

Reference

Moyle J.R., R.F. Wideman, S.M. Whipple, D.E. Yoho and R.K. Bramwell. 2011. Urolithiasis in male broiler breeders. International Journal of Poultry Science 10(11): 839-841.

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