VetSRev
Database of veterinary systematic reviews
Database of veterinary systematic reviews
Animal Feed Science and Technology (2012) 171: 31–42
DOI: 10.1016/j.anifeedsci.2011.09.017
Studies used to evaluate effects of dietary intervention on fertility may be subject to confounding because modification of one nutritional input requires a change in at least one other input. Meta-analytical modeling allows examination of a main intervention for a series of studies, but also an examination of a series of related effects through use of meta-regression. Effects of dietary crude protein (CP) on fertility were examined using this approach. We obtained 21 studies containing 32 comparisons that had pregnancy or conception data and met the eligibility criteria for meta-analysis of randomized controlled experiments providing information on diets used. Publications that contained data on prospective, randomized controlled experiments examining effects of dietary CP, either concentrations or degradability, or effects of a specific feed ingredient intervention on fertility were identified. Details on dietary formulation and diet intake were extracted from the publications, as were measures of urea in blood or plasma. Estimated fixed and random effects relative risks showed that risk of conception was lower in cows fed higher CP or more degradable CP diets (fixed effect (Mantel-Haenszel Relative Risk)=0.91 (95% CI 0.84-0.98); _P_=0.019). This effect was homogenous (_I_²=0) and not influenced by difference in blood urea N, duration of intervention, breed, parity, milk production or type of diet delivery. Significant associations among CP components of the diet and carbohydrate fractions supported the hypothesized potential for confounding, but only the amount of soluble CP eaten was a significant meta-regression covariate that reduced risk of conception. There was no evidence that the significant reduction in fiber or non-fiber carbohydrate (NFC) fractions of the diets associated with increased concentration of CP, soluble CP or rumen degradable fractions or soyabean products content of the diet influenced conception rates. Results support findings of experiments showing that increased intake of soluble CP reduced conception rates, and provides strong evidence that increased concentrations of CP or increased degradability of CP, within the ranges evaluated in the studies contributing to this meta-analysis, reduce the risk of conception in lactating dairy cattle.
Lean, I. J., Celi, P., Raadsma, H., McNamara, J., & Rabiee, A. R. (2012). Effects of dietary crude protein on fertility: meta-analysis and meta-regression. Animal Feed Science and Technology, 171(1), 31–42. https://doi.org/10.1016/j.anifeedsci.2011.09.017 pregnancy, [Indexed using CAB Thesaurus terms], Animal Husbandry and Production [LL180], Animal Physiology and Biochemistry (Excluding Nutrition) [LL600], Animal Reproduction and Embryology [LL250], animals, Artiodactyla, Chordata, eukaryotes, gestation, mammals, ungulates, vertebrates, Bos, Bovidae, cattle, cows, dairy cattle, dairy cows, meta-analysis, ruminants, Animal Genetics and Breeding [LL240], Animal Nutrition (General) [LL500], Animal Nutrition (Physiology) [LL510], Dairy Animals [LL110], diets, rumen, blood, data analysis, research, studies, fiber, fibre, angiosperms, animal breeding, animal nutrition, blood chemistry, comparisons, composition, conception rate, Crop Produce [QQ050], crude protein, dicotyledons, Fabaceae, Fabales, feeding stuffs, feeds, fertility, Field Crops [FF005], Forage and Feed Products (Non-human) [RR000], Glycine (Fabaceae), intake, milk, Milk and Dairy Produce [QQ010], milk production, models, modification, Papilionoideae, plants, soyabean products, soyabeans, soybean products, soybeans, Spermatophyta, urea, yields