Sustainable intensive farming systems

Sustainable intensive farming systems By: Garnsworthy, P. C. Edited by: Casasus, I; Rogosic, J; Rosati, A; Stokovic, I; Gabina, D ANIMAL FARMING AND ENVIRONMENTAL INTERACTIONS IN THE MEDITERRANEAN REGION Book Series: EAAP European Association for Animal Production Publication Issue: 131 Pages: 139-143 Published: 2012 Conference: 11th International Mediterranean Symposium on Animal Farming and Environment Interactions in Mediterranean Region Location: Zadar, CROATIA Date: OCT 27-29, 2010 Publisher WAGENINGEN ACAD PUBL, POSTBUS 220, 6700 AE WAGENINGEN, NETHERLANDS The following paper is the author s final accepted version. For more information, please contact Phil.Garnsworthy@nottingham.ac.uk 1

Sustainable Intensive Farming Systems P.C. Garnsworthy University of Nottingham, School of Biosciences, Sutton Bonington Campus, Loughborough LE12 5RD, UK. Phil.Garnsworthy@nottingham.ac.uk Abstract Dairy systems contribute 20 to 30% of livestock emissions and excretions in Europe. Cows convert food unsuitable for human consumption (grass, forages, byproducts) into high quality food (milk), but nutrient conversion is 20 to 30%, so 70 to 80% of nutrients are excreted. With indoor systems, wastes can be contained and spread on the land when plant uptake is optimal. The main driver of environmental impact is production efficiency, i.e. milk or wastes per unit input. Efficiency is a function of animal numbers (milking cows and replacements), milk yield and culling rate. Higher-yielding fertile cows produce more milk per lactation and lifetime, so unproductive emissions and excretions for maintenance and rearing are spread over more litres of milk. Poor fertility in modern dairy cows increases culling, which offsets efficiency gains from high milk yield. Our recent work has studied nutrition, insulin and fertility. Insulin stimulates oestrous cycles, but reduces oocyte quality. Dietary manipulation of insulin at strategic phases of the reproductive cycle doubled the proportion of cows pregnant at 120 days in milk. Diets for high-yielding cows contain more concentrates, starch and fat, and less fibre than grass-based systems, which reduce methane emissions. Breeding for low methane emissions may be possible in future; we find variation among cows with the same milk yield and diet. Nitrogen and phosphorus excretions are reduced by increasing production efficiency and by reducing excess inputs. Scope for reducing excesses is greater in higher-yielding cows, but trade-off in nitrous oxide emissions must be avoided. A whole-system approach is needed which considers environmental cost of diet formulation as well as economics. Introduction With policy drives to reduce environmental impacts of livestock systems, increasing attention is being paid to greenhouse gas emissions and excretion of nitrogen and phosphorus. This paper focuses on intensive dairy systems to illustrate ways to reduce impacts. Some of the principles apply to other livestock systems, but non-ruminants make a smaller contribution to total impacts and extensive systems provide less scope for mitigation (Garnsworthy, 2004b). Estimates vary, but dairy systems in Europe contribute between 20 and 30% of methane emissions (Garnsworthy, 2004a; CE Delft, 2008) and similar proportions of nitrogen and phosphate excretions (Table 1). The dairy cow is very efficient at converting foods unsuitable for human consumption (e.g. grass, forages, by-products) into a high quality food product (milk). Wilkinson (2010) calculated that an average dairy cow yields 2.37 MJ of human-edible energy per MJ of human-edible energy intake and 1.64 kg of human-edible protein per kg human-edible protein intake. In terms of total nutrient efficiency, however, the cow is not so good only 20 to 30% of nutrients consumed are converted into product; the remaining 70 to 80% are released to the environment. 2

Table 1. EU livestock numbers and estimated excretions of nitrogen and phosphate 1. million head Nitrogen Phosphate 2007 kg/head/yr Mt/yr % total kg/head/yr Mt/yr % total Dairy cows 24 94 2.2 32 37 0.9 25 Beef cows 12 60 0.7 11 22 0.3 8 Cattle <1 yr 25 12 0.3 4 3 0.1 2 Cattle 1-2 yr 19 47 0.8 13 8 0.2 4 Cattle >2 yr 9 55 0.4 7 12 0.1 3 Breeding sheep/goats 55 9 0.5 7 6 0.3 10 Growing sheep/goats 58 3 0.2 3 3 0.2 5 Breeding pigs 16 14 0.2 3 17 0.3 8 Growing pigs 92 9 0.8 12 7 0.7 18 Broilers 780 0.5 0.4 6 0.5 0.4 10 Layers 469 0.6 0.4 4 0.5 0.3 7 6.9 3.5 1 Data sources: Eurostat; IPCC; Barnett (1994); Author s own estimates. Production Efficiency Whether the environmental impact of animal systems is calculated as total impact or impact per unit of product, the main driver of impact is production efficiency. Production efficiency is the converse of impact efficiency and, for dairy systems, is the overall output of milk or pollutants per unit of input. Efficiency in both cases is directly related to animal numbers (both lactating cows and replacement heifers), which are in turn related to milk yield per cow (Figure 1) and replacement rate i.e. lifetime output per cow. Number of cows 300 250 200 150 100 50 cows efficiency 0.30 0.25 0.20 Energetic efficiency 0 4000 5000 6000 7000 8000 9000 10000 Milk yield (kg/cow/year) Figure 1. Influence of annual milk yield per cow on number of cows required to produce one million litres of milk and overall energetic efficiency (Net energy output over gross energy intake). 0.15 3

Higher-yielding cows produce more milk per lactation and fertile cows survive for more lactations. This means that unproductive emissions and excretions for maintenance and the rearing phase are spread over more units of milk across the lifetime (Table 2). Table 2. Lifetime milk yield, methane emissions and nitrogen excretion of cows surviving for three or four lactations 1. Lactations 3 4 3 vs 4 Milk yield (t) 22.7 28.9 +27% Methane (GJ) 39.1 44.2 +13% Methane (MJ/l) 1.72 1.53-13% Nitrogen (kg) 341 435 +28% Nitrogen (kg/l) 15.02 15.05 +0.2% 1 Data for average cows from Garnsworthy (2004a) There has been a trend in most countries of the world over the past 30 years for increased milk yield per cow. Approximately 50% of this is due to genetics and 50% to improved feeding and management (Pryce et al., 2004). Since the introduction of EU milk quotas in 1984, cow numbers in the UK, as in most of Europe, have declined whilst total milk supply has remained relatively constant. Projecting the rate of change in milk yield and cow numbers to 2050 suggested that methane emissions will reduce by 47% of 1990 values (Garnsworthy, 2004b), although this figure was revised subsequently to 31% (Garnsworthy: unpublished). There is a major obstacle to achievement of this reduction in emissions. As genetic merit for milk yield has increased, there has been an accompanying decline in fertility (Royal et al., 2000). The result is that replacement rate has increased, so there are increased numbers of nonproductive youngstock and each cow has a lower lifetime performance. Consequently, methane emissions are projected to decline by only 19% unless the fertility issue is addressed. Garnsworthy (2004a) modelled the effect of fertility on methane and ammonia emissions by dairy herds; at current levels of fertility, replacements contribute 27 % of methane emissions and 15 % of ammonia emissions in a high-yielding herd, but these could be reduced to 15 % and 8 % if fertility was restored to ideal levels. If fertility could be restored, projected reductions in methane emissions by 2050 would be 36%. Having identified the fertility issue in the late 1990s (Webb, et al., 1999), we embarked on a ten-year programme to study nutritional effects on fertility in dairy cows. The main priorities identified are to minimise negative energy balance in early lactation and to maintain adequate plasma insulin concentrations at strategic phases of the reproductive cycle (Garnsworthy et al., 2008). The main driver of negative energy balance is body condition score (BCS) at calving because cows calving above BCS 3.0 will have reduced appetite and mobilise in excess of 1 BCS unit, with detrimental effects of fertility (Garnsworthy & Topps, 1982; Garnsworthy et al., 2008a). Our early work demonstrated that diet-induced increases in postpartum insulin status could increase the proportion of cows ovulating during the first 50 days of lactation (Gong et al., 2002). Subsequent studies, however, showed that high insulin can have detrimental effects on oocyte quality, which would decrease pregnancy rate (Garnsworthy et al., 2008). In a concept experiment, we fed cows on an insulin-stimulating diet (high starch, low fat) immediately postpartum and then changed to an insulin-reducing diet (high fat, low starch) after cows started 4

to cycle (Garnsworthy et al., 2009). Compared with continuous feeding of either diet or the reverse strategy (low high insulin), there was a significant improvement in the proportion of cows pregnant at 120 days of lactation (from 27% to 60%). A recent study in New Zealand found a similar response in grazing dairy cows (Burke et al., 2010). Nutritional Mitigation In addition to reducing the number of animals used to meet milk supply requirements, there are some opportunities to reduce emissions and excretions per cow. Methane is produced by archaea during rumen fermentation of cellulose. This is an essential metabolic function to maintain rumen ph and fermentation of forages. However, there is scope for altering fermentation by changing the proportion of concentrates in the diet and increasing dietary starch or fat content at the expense of fibre content. The net effect is a reduction in rumen hydrogen production and, therefore, reduced conversion to methane. Researchers have been striving since the 1960s to find a reliable methane inhibitor. With the possible exception of ionophores, which are banned in Europe, promising results in vitro have not been translated into practical mitigation strategies (Beauchemin et al., 2008). The rumen microbial ecosystem is extremely adaptable and short-term perturbations are overcome within a few days or weeks. Often effective methane inhibitors have detrimental effects on overall microbial efficiency. The major strategy remains, therefore, to increase production efficiency and to reduce reliance on grass. Possible strategies for the future include genetic selection for feed efficiency (measured as residual feed intake) and genetic selection for individual methane production. We are currently conducting a study of variation among cows in the frequency of eructation and concentration of methane in breath; even cows fed on the same diet and producing the same quantity of milk vary in methane emissions. Nitrogen excretion per unit product can also be reduced by increasing production efficiency. Excretion per cow is directly related to dietary nitrogen content and excess nitrogen is increasingly excreted in urine, which has greater pollution potential than organic nitrogen found in faeces. The scope for reducing nitrogen content of diets, without compromising milk production, is greater in higher-yielding cows. Even so, the most efficient cows still excrete approximately 70% of nitrogen consumed. The major challenge is to minimise excretion of the volatile (urine) form and to reduce losses during housing and spreading of manure. Dairy cows can survive on very low phosphorus diets because of an extremely efficient recycling system via the saliva (Ferris, 2010). Excess phosphorus is excreted in faeces, with very little being excreted in urine. Nutritionists are reluctant to reduce dietary phosphorus content because of implications for health and production. However, after production efficiency, this would be the main strategy for reducing phosphorus pollution by dairy cows. Non-dairy systems Production efficiency also influences environmental impact of intensive meat and egg production systems. Growth rate or egg yield, feed efficiency, mortality and reproductive performance all influence overall product output per unit input and per unit of emissions. In egg production, for example, average yield is predicted to reach 360 eggs per bird per year before 2030, which will reduce nitrogen excretion by 24% compared with current production levels (Garnsworthy, 5

2004b). Growth rate of pigs is predicted to be 28% faster in 2050, which will reduce the number of days to slaughter by 22% and overall nitrogen excretion by 14% (Garnsworthy, 2004b). Optimising amino acid balance for growing pigs, particularly with the inclusion of synthetic amino acids, can reduce nitrogen excretion by up to 40% (Verstegen and Tamminga, 2002). As in the dairy herd, replacement rate in the pig breeding herd has been increasing due to reproductive failure, particularly of animals in parities 1 and 2 (Hughes and Varley, 2003). The annual replacement rate in the UK pig herd increased from 36% in 1980 to 43% in 2003, requiring an increase of 17% in the number of gilts reared per year, which is equivalent to an extra 360 tonnes of nitrogen excreted per year. Conclusions In conclusion, the main strategy for reducing the environmental footprint of intensive livestock systems must be to reduce wastage of breeding animals through premature culling for fertility and diseases. Coupled with this is increased production efficiency through use of animals with higher genetic merit for milk yield, growth rate or egg production. Both of these approaches will reduce the proportions of energy and protein used for unproductive functions, such as maintenance and rearing, and should also improve profitability. Care must be taken to avoid increased use of cereal-based concentrates, however, which compete as human food and lead to greater emissions of nitrous oxide. In fact, every mitigation strategy involves a trade-off of some sort. Therefore, a whole-system approach is needed which considers the environmental cost of diet formulation as well as the economic cost. References Barnett, G.M., 1994. Phosphorus forms in animal manure. Bioresource Technology, 49: 139-147. Garnsworthy, P.C., 2004a. The environmental impact of fertility in dairy cows: a modelling approach to predict methane and ammonia emissions. Animal Feed Science and Technology, 112: 211-223. Beauchemin, K.A., M. Kreuzer, F. O Mara & T.A. McAllister, 2008. Nutritional management for enteric methane abatement: a review. Australian Journal of Experimental Agriculture, 48: 21 27. Burke, C.R., J.K. Kay, C.V.C. Phyn, S. Meier, J.M. Lee & J.R. Roche, 2010. Short communication: Effects of dietary nonstructural carbohydrates pre- and postpartum on reproduction of grazing dairy cows. Journal of Dairy Science, 93: 4292 4296. Ferris, C.P., 2010. Reducing dietary phosphorus inputs within dairy systems. In: Recent Advances in Animal Nutrition 2009, P.C. Garnsworthy & J. Wiseman (editors), Nottingham University Press, Nottingham, p 49-75. Garnsworthy, P.C., 2004b. Livestock yield trends: implications for animal welfare and environmental impact. In: Yields of Farmed Species, J. Wiseman & R. Sylvester-Bradley (editors), Nottingham University Press, Nottingham, p 379-401. Garnsworthy, P.C., A.A. Fouladi-Nashta, G.E. Mann, K.D. Sinclair & R. Webb, 2009. Effect of dietary-induced changes in plasma insulin concentrations during the early postpartum period on pregnancy rate in dairy cows. Reproduction, 137: 759-768. 6

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