No abstract

The pivotal roles of regulatory jurisdictions in the feed additive sector cannot be over-emphasized. In the European Union (EU), antioxidant substances are authorized as feed additives for prolonging the shelf life of feedstuffs based on their effect for preventing lipid peroxidation. However, the efficacy of antioxidants transcends their functional use as technological additives in animal feeds. Promising research results have revealed the in vivo efficacy of dietary antioxidants for combating oxidative stress in production animals. The in vivo effect of antioxidants is significant for enhancing animal health and welfare. Similarly, postmortem effect of dietary antioxidants has been demonstrated to improve the nutritional, organoleptic and shelf-life qualities of animal products. In practice, dietary antioxidants have been traditionally used by farmers for these benefits in livestock production. However, some antioxidants particularly when supplemented in excess could act as prooxidants and exert detrimental effects on animal well-being and product quality. Presently, there is no exclusive legislation in the EU to justify the authorization of antioxidant products for these in vivo and postmortem efficacy claims. To indicate these efficacy claims and appropriate dosage on product labels, it is important to broaden the authorization status of antioxidants through the appraisal of existing EU legislations on feed additives. Such regulatory review will have major impact on the legislative categorization of antioxidants and the efficacy assessment in the technical dossier application. The present review harnesses the scientific investigations of these efficacy claims in production animals and, proposes potential categorization and appraisal of in vivo methodologies for efficacy assessment of antioxidants. This review further elucidates the implication of such regulatory review on the practical application of antioxidants as feed additives in livestock production. Effecting these regulatory changes will stimulate the innovation of more potent antioxidant products and create potential new markets that will have profound economic impacts on the feed additive industry. Based on the in vivo efficacy claims, antioxidants may have to contend with the legislative controversy of either to be considered as veterinary drugs or feed additives. In this scenario, antioxidants are not intended to diagnose or cure diseases as ascribed to veterinary products. This twisted distinction can be logically debated with reference to the stipulated status of feed additives in Commission Regulation (EC) No 1831/2003. Nonetheless, it is imperative for relevant stakeholders in the feed additive industry to lobby for the review of existing EU legislations for authorization of antioxidants for these efficacy claims.

The particle size of the forage has been proposed as a key factor to ensure a healthy rumen function and maintain dairy cow performance, but little work has been conducted on ryegrass silage (GS). To determine the effect of chop length of GS and GS:maize silage (MS) ratio on the performance, reticular pH, metabolism and eating behaviour of dairy cows, 16 multiparous Holstein-Friesian cows were used in a 4×4 Latin square design with four periods each of 28-days duration. Ryegrass was harvested and ensiled at two mean chop lengths (short and long) and included at two ratios of GS:MS (100:0 or 40:60 dry matter (DM) basis). The forages were fed in mixed rations to produce four isonitrogenous and isoenergetic diets: long chop GS, short chop GS, long chop GS and MS and short chop GS and MS. The DM intake (DMI) was 3.2 kg/day higher (P<0.001) when cows were fed the MS than the GS-based diets. The short chop length GS also resulted in a 0.9 kg/day DM higher (P<0.05) DMI compared with the long chop length. When fed the GS:MS-based diets, cows produced 2.4 kg/day more (P<0.001) milk than when fed diets containing GS only. There was an interaction (P<0.05) between chop length and forage ratio for milk yield, with a short chop length GS increasing yield in cows fed GS but not MS-based diets. An interaction for DM and organic matter digestibility was also observed (P<0.05), where a short chop length GS increased digestibility in cows when fed the GS-based diets but had little effect when fed the MS-based diet. When fed the MS-based diets, cows spent longer at reticular pH levels below pH 6.2 and pH 6.5 (P<0.01), but chop length had little effect. Cows when fed the MS-based diets had a higher (P<0.05) milk fat concentration of C18 : 2n-6 and total polyunsaturated fatty acids compared with when fed the GS only diets. In conclusion, GS chop length had little effect on reticular pH, but a longer chop length reduced DMI and milk yield but had little effect on milk fat yield. Including MS reduced reticular pH, but increased DMI and milk performance irrespective of the GS chop length.

The particle size of the ration has been proposed as a key factor, along with its fibre and non-forage carbohydrate concentration, to ensure healthy rumen function and optimal performance of dairy cows. The current particle size distribution recommendations for forages and rations are primarily based on lucerne-haylage and maize silage (MS) and may not be suitable for the wetter grass silage (GS) based rations typically fed in Northern Europe. In order to characterize the particle size distribution of forages and rations in the UK, fifty commercial dairy herds feeding a range of GS and MS based rations were sampled during the winter of 2015/2016. The particle size distribution of the fresh forages and mixed rations (MR; total and partial mixed rations) were analysed using a modified Penn State Particle Separator with six screens of hole size 60, 44, 26.9, 19, 8, and 4 mm. The fresh MR was collected at 5-equally-spaced locations along the length of the feed-face for each herd within 5-min of feeding to determine the consistency of ration mixing, and again from the same locations 4h post-feeding. Grass silage was the main forage fed on 50 herds, with 80.3% of the dry matter (DM) being retained above the 19 mm sieve, which is considerably higher than the North-American recommendations for lucernehaylage. The particle size distribution of MS followed the general recommendations for North American forages, however, the 8-19 mm fraction was higher and the <4 mm lower. The >60 mm fraction of the MR had the lowest (0.1% DM) DM retention, and the 8-19 mm fraction the highest (34.9% DM). The MR had a higher proportion of particles retained on the 26.9 mm sieve when GS was the sole forage. Fifty eight % of herds were considered to have either moderately or poorly mixed rations, whilst 66% had evidence of diet selection 3 (either preferential consumption or selective refusals). Particle size of the MR accounted for 33% of the variance in the milk fat content and 12% of milk yield. In conclusion, the particle size distribution of the GS and MR fed on UK dairy herds is different from the current recommendations, suggesting that the particle size of UK dairy rations is too long or new guidelines using additional sieves with larger pore sizes are required. There is also a high proportion of herds with poor mixing and/or evidence of diet selection.

No abstract