Fish meal supplementation to early lactation Jersey cows grazing ryegrass pasture

 

 

E.R. Malleson^I; R. Meeske^II; L.J. Erasmus^I; W.A. Van Niekerk^I; R.J. Coertze^I

^IDepartment of Animal & Wildlife Sciences, University of Pretoria, Pretoria 0002, South Africa
^IIDepartment of Agriculture, Western Cape, Outeniqua Experimental Farm, P.O. Box 249, George 6530, South Africa

Correspondence

 

 

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ABSTRACT

This trial was conducted to test the hypothesis that early lactation cows grazing ryegrass pasture and receiving maize and mineral supplementation could respond to additional supplementation with a protein source such as fish meal. Multiparous Jersey cows in early to mid lactation that grazed annual ryegrass pasture in spring were used in a randomised complete block design experiment. In addition to the pasture, cows received 6 kg (as is) of a maize-based supplement, including minerals, fed in two equal portions in the milking parlour. Three groups of 15 cows received a control, a low fish meal or a high fish meal treatment (0, 4 or 8% fish meal replacing maize). Milk yield was measured and milk samples taken fortnightly. A simultaneous study on rumen fermentation was conducted using eight rumen cannulated cows receiving the control and high fish meal treatments in a cross-over design experiment. Ruminal pH and ammonia-N and volatile fatty acid concentrations were measured. Milk yield, 4% fat-corrected milk yield and milk fat and protein percentages of cows on the low and high fish meal treatments (21.9 and 22.1 kg milk/d, 24.1 and 24.2 kg 4% fat corrected milk/d, 4.73 and 4.67% fat and 3.49 and 3.45% protein) were higher than the control (20.5 kg milk/d, 20.4 kg 4% fat corrected milk/d, 3.97% fat and 3.25% protein). The ruminal ammonia-N concentration was higher in the cows on the high fish meal treatment than the control (16.7 vs. 14.2 mg/dL). Fish meal supplementation to cows on ryegrass proved to be profitable.

Keywords: Dairy cattle, cultivated pasture, RUP, maize, milk yield, milk composition

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Introduction

Many pasture-based dairy farmers in the Southern Cape region of South Africa supplement only maize and minerals to grazing dairy cows as this is seen to be the most economical (Rubin, R., Personal communication, jackrubin@mweb.co.za). Lush pasture, such as ryegrass, has a high content of crude protein (CP) that is highly degradable in the rumen (McCormick et al. 1999; 2001b; Bargo et al., 2003). Metabolisable energy (ME) is the first limiting nutrient for cows grazing high quality pasture (Muller & Fales, 1998; Bargo et al., 2002b; Kolver, 2003). However, at higher levels of supplementation and when milk production is high, specific amino acids (AA), particularly methionine (Met) and lysine (Lys), may limit milk production (Kolver et al., 1998b; Muller & Fales, 1998; Kolver, 2003). For a high yielding cow, especially in early lactation, a smaller proportion of the protein is generally supplied by the rumen microbes and more needs to escape rumen degradation than would be the case with lower genetic merit cows (Hongerholt et al., 1998; Santos et al., 1998; Schroeder & Gagliostro, 2000).

Most previous studies, where cows were grazing on various types of pasture and were supplemented with concentrate, were conducted with Holstein cows. Increasing rumen-undegradable protein (RUP), or replacing rumen-degradable protein (RDP) sources with RUP sources, in concentrates has not had a consistent effect on milk production or composition (Carruthers et al., 1997; Santos et al., 1998; Bargo et al., 2003). In several studies RDP sources such as soyabean meal, sunflower meal, urea or rapeseed meal have been replaced with RUP sources such as animal protein blend, fish meal (FM), maize gluten meal, expeller soyabean meal, blood meal, feather meal or heat-treated rapeseed meal (Bargo et al., 2003). Lactation studies with cows grazing pasture that reported an increase in milk production were those of Schroeder & Gagliostro (2000) and Schor & Gagliostro (2001) where the milk response was 6 and 18%, respectively, above the control. (In the former study cows grazed a mixture of lucerne, red clover, orchardgrass and perennial ryegrass. In the latter study cows grazed a mixture of perennial ryegrass, red and white clover and orchardgrass). Menhaden FM was the RUP source that most frequently increased milk yield compared to soyabean meal and is also ranked highest in essential amino acid (EAA) index, indicating that the type of RUP supplement (AA profile) is more important than the amount of RUP (Santos et al., 1998). Positive responses to RUP supplementation, above that observed with energy, are most likely in early lactation, high yielding, multiparous cows, when high amounts of concentrate grain are fed (Hongerholt & Muller, 1998; Schor & Gagliostro, 2001).

Fish meal was used in this study as a quality protein source since it is recognised as an excellent source of RUP, rich in Lys and Met which are probably the first and second limiting AA for milk yield and milk protein synthesis (Rulquin & Vérité, 1993; Santos et al., 1998; Schroeder & Gagliostro, 2000).

Pastures of kikuyu (Pennisetum clandestinum) over-sown with annual ryegrass (Lolium multiflorum) are common in the Southern Cape. The former species, adapted to hot climates, is active in summer, complementing the latter, which is used for winter grazing. This trial was conducted on annual ryegrass in spring. The milk yield potential of 500 kg cows grazing ryegrass pasture, with no supplementation, is 16 to 17 litres a day (Dugmore, 1995).

The aim of the study was to determine whether grazing cows that are receiving maize supplementation, with minerals included, would respond to the addition of a high quality protein source, such as FM, to their supplement.

 

Materials and Methods

Forty five multiparous Jersey cows [body weight, 331 ± 29.9 kg; milk yield, 21.4 ± 1.65 kg/d; parity, 4.1 ± 1.53; days in milk, 73 ± 28.3; (mean ± s.d.)] from the Outeniqua Experimental Farm (Longitude 22°25', latitude 33°57', altitude 190 m), near George in the Southern Cape, South Africa, were used. The long-term (39 y) average rainfall in this area is 725 mm per annum. The mean daily maximum and minimum temperatures during the experimental period of the trial were 21 and 11 °C, respectively. The average milk production of the herd of 326 cows in lactation from which the cows were selected was 17.0 kg/d in August 2005. The higher producing, early to mid lactation, cows from the herd were selected for the trial.

A randomised complete block design was used. Just before the experimental period the cows were blocked according to milk production (of the previous 25 days) and days post calving and within each block were randomly divided into three groups. These three groups were randomly allocated to three experimental treatments.

The cows strip-grazed annual Westerwold ryegrass (Lolium multiflorum, Energa cv, fertilised with 56 kg N (limestone ammonium nitrate) per ha after each grazing, and were moved to a new strip twice a day after each milking. The cows were milked at 06:00 and 14:30 in a 20 point Dairy Master (Total Pipeline Industries, 33 Van Riebeeck St., P.O. Box 252, Heidelberg 6665, RSA) swing over milking machine with weigh-all electronic milk meters. The cows grazed all hours (except for the milking times) and clean drinking water was available ad libitum. All the cows were grazed together as a single herd to ensure equal pasture allocation. The mean daily pre-grazing pasture allowance was 11 kg dry matter (DM) per cow per day above 3 cm pasture height (based on previous experience with pasture management of the herd), measured with a rising plate meter (Filip's folding plate pasture meter, Jenquip, Rd 5, Fielding, New Zealand). The rising plate meter was calibrated to the pasture used in the trial by measuring three low, medium and high pasture heights and cutting the grass under the plate to 3 cm above the ground. The samples were dried at 60 °C for 72 hours. The linear regression equation, Y = 62 H - 57 (R² = 0.4; n = 90) was fitted to the data, where Y is pasture yield (kg DM/ha) and H = pasture height on the rising plate meter.

The average pasture height, before and after grazing, of each pasture strip was measured by taking 100 rising plate meter readings. The post grazing pasture height was used to estimate the pasture intake at 7.6 kg DM/cow/d. This, however, must have been an underestimate as the cows would not likely have been able to produce the amount of milk they did with this pasture intake (based on modelling with CPM Dairy (Version 3.0.7a; Cornell University, Ithaca, NY, University of Pennsylvania, Philadelphia, PA; Willam H. Miner Agricultural Institute, Chazy, NY)). The mean pasture intake of the cows was assumed to be 8.6 kg pasture DM per day, based on the assumption that cows on pasture-concentrate can consume 1.3% of body weight (BW) as neutral detergent fibre (NDF) (Vazquez & Smith, 2000; Bargo et al., 2002b). The expected NDF intake of the cows was calculated as 1.3% of the average BW of all the cows between the beginning and end of the trial, the NDF consumed in the concentrate subtracted, and then the pasture dry matter intake (DMI) calculated based on the known NDF content of the pasture.

In addition to the pasture the cows each received 6 kg (as is, 5.5 kg DM) of pelleted concentrate per day, divided into two equal portions and fed in the milking parlour. The cows in the three groups each received a different concentrate (Table 1). The pellets of the cows on the control treatment contained no FM. For the two FM treatments some of the maize was replaced by FM: 4% (240 g FM/cow/d) for the low FM treatment and 8% (480 g FM/cow/d) for the high FM treatment. Table 2 shows the chemical composition of the fish meal used. The diets were formulated to be iso-energetic. Megalac (a rumen protected fat; Church & Dwight Co., Inc., 469 N. Harrison St., Princeton, NJ 08543-5297) was added to the latter two treatments to bring the energy to the same level in all three concentrates. The CP concentrations of the diets differed since it is the effect of additional protein that was to be investigated. The molasses was added to facilitate pelleting which was done to increase the palatability.

 

 

Representative samples of pasture (cut to 3 cm above the ground as the cows grazed to almost this level) and concentrate (there were negligible feed refusals) were taken weekly and milled through a 1 mm screen. These were analysed at the UP-Nutrilab (Department of Animal and Wildlife Sciences, University of Pretoria, Pretoria) for DM (AOAC, 2000, procedure 934.01), ash (AOAC, 2000, procedure 942.05), CP (N was determined using a Leco N analyser, model FP-428, Leco Corporation, St Joseph, MI, USA and CP was calculated as N x 6.25), NDF (Robertson & Van Soest, 1981), acid detergent fibre (ADF; Goering & Van Soest, 1970), in vitro organic matter digestibility (IVOMD; Tilley & Terry, 1963 as modified by Engels & Van der Merwe, 1967). Every three pasture samples were composited and these, along with the concentrate samples, were analysed for gross energy (GE; MC - 1000 Modular Calorimeter, Operators Manual), ether extract (EE; crude fat; AOAC 2000, procedure 920.39), Ca (AOAC 2000, procedure 965.09), P (AOAC 2000, procedure 965.17) and AA composition (with the PICOTag method (Bidlingmeyer et al., 1984) using a Waters HPLC with two Model 510 pumps, UV protector Model 440, autosampler Model 712 and Waters Millennium 32 software). Metabolisable energy was calculated with the following formula: ME (MJ/kg DM) = 0.82 x (GE x IVOMD) (Robinson et al., 2004).

After an adaptation period of 12 days, milk yield was measured in the milking parlour for 46 days. Composite milk samples (ratio 9 mL : 15 mL afternoon : morning milking) were taken every second week and analysed for fat, protein, lactose and milk urea nitrogen (MUN) at Lactolab Pty (Ltd) (ARC, Main rd., Irene, 0062) using the Milkoscan FT 6000 (Foss Electric, Denmark). Fat-corrected milk (FCM) yield was calculated using the following formula: 4% FCM = 0.4 x kg milk + 15 x kg milk fat (NRC, 2001).

At both the beginning and end of the trial the cows were weighed on two consecutive days and the mean of the body weights recorded on these two days was determined. Body condition score (BCS) was determined on the first of these two days using the five point system where 1 is thin and 5 is fat (Wildman et al., 1982).

Concurrent with the milk production study changes in rumen fermentation patterns of cows were determined by using eight Jersey cows fitted with rumen cannulae (with rolled inner flange 10 cm in diameter; Bar Diamond, Inc., P.O. Box 60, Parma, Idaho, USA). These cows grazed, were milked and received concentrate with the cows of the production study. A cross-over design was used. Four of the cows (chosen at random) received the control treatment and four of them the high FM treatment. After an adaptation period of 19 days, the cows were fitted with automated pH meters with data loggers (WTW pH 340i pH meter/ data logger with a WTW SenTix 41 pH electrode) so that the ruminal pH at 10 min intervals throughout the day could be monitored. The electrode was placed in the rumen via the cannula and connected to the data logger that was strapped on like a saddle. The pH in the rumen of each cow was monitored for a total of four days. Samples of ruminal fluid were taken over a period of three days, with at least eight hours between two consecutive sampling times, such that in the end there were samples representing every four hours of the day (00:00, 04:00, 08:00, 12:00, 16:00 and 20:00). From each sample 30 mL of rumen filtrate was preserved with 5 mL 50% H₂SO₄ and frozen for ammonia-N (NH₃-N) analysis (De Bruin, 1995) and 20 mL of rumen filtrate was preserved with 4 mL of 25% H3PO4 and frozen for volatile fatty acid (VFA) analysis (Beauchemin et al., 2003). These were analysed for NH₃-N (Broderick & Kang, 1980) and VFA (acetic, propionic, butyric, iso-butyric and valeric acids; Webb, 1994, with modifications) at the UP-Nutrilab. On day 30 of the trial the cows were switched to the opposite experimental treatment (those that were on the control treatment received the high FM treatment and vice versa) so that in the end each cow received both treatments and there were eight cows per treatment.

An analysis of variance with the ANOVA model (SAS, 2001) was used to determine the difference between the experimental treatments in terms of milk yield and composition, FCM, change in BW and BCS and mean daily ruminal pH, NH₃-N and VFA. Cows were used as replicates. Significance of difference was determined using Duncan's test (Samuels, 1989). Difference was considered significant at P <0.05 and highly significant at P <0.01. Tendency was indicated at P <0.10.

 

Results and Discussion

The chemical composition of the pasture (Table 3) was in the range expected for annual ryegrass (Fulkerson et al., 1998; 2005; McCormick et al., 2001b; Marais et al., 2003; Granzin, 2004; Meeske et al., 2006). The main difference between the three experimental treatments was the CP concentration of the supplements: 82, 112 and 146 g/kg for the control, low FM and high FM treatments, respectively (Table 3).

Although the EE increased slightly with the inclusion of FM, the ME of the three concentrates was similar. There is no clear explanation as to why the IVOMD, and hence ME, was higher in the low FM concentrate than the other two.

The total diets of the cows on all three treatments were adequate in all the main nutrients (assuming an average pasture intake of 8.6 kg DM/cow/d). The CP (192, 203 and 216 g/kg DM for the control, low FM and high FM diets, respectively) was adequate for a production of more than 20 kg milk a day (NRC, 2001). Including FM in the concentrate increased both RDP and RUP in the diet, based on the assumption that the RUP of the maize was 43% of CP (NRC, 2001) and the RUP of the FM was 62% of CP (Table 2). Each successive FM level would have supplied an additional 90 g RUP/d to diet. The diets contained 6.7 g Lys/kg DM and 0.7 g Met/kg DM (94 g Lys and 10 g Met per day) for the control treatment, 7.4 g Lys/kg DM and 1.1 g Met/kg DM (105 g Lys and 16 g Met per day) for the low FM treatment and 7.8 g Lys/kg DM and 1.8 g Met/kg DM (111 g Lys and 25 g Met per day) for the high FM treatment. Thus, both Lys and Met increased as the level of FM in the concentrate increased, especially Met. The high FM treatment comes closest to the ideal Lys : Met ratio of 3.0 : 1 (NRC, 2001).

The effect of including different levels of FM in the diets of Jersey cows is presented in Table 4. The cows on the low FM treatment responded by producing 7% more milk, yielding 28% more milk fat, yielding 13% more milk protein and producing 18% more 4% FCM than the cows on the control treatment. Milk yield, 4% FCM yield and milk fat, protein and lactose percentages of cows on the low and high FM treatments were higher than the control (P <0.01). There was no additional benefit to the higher level of FM as the two FM treatments did not differ from each other in terms of the above parameters (P >0.10).

In the review of Bargo et al. (2003) it was stated that there is an average increase in milk production of 0.8 kg/d for each 100 g/d of RUP. Since the low FM diet supplied an estimated additional 90 g RUP/d, the milk response was approximately 1.5 kg milk per 100 g additional RUP supplementation, almost double the level reported by Bargo et al. (2003). This could be related to the excellent AA profile of FM since the AA profile of the RUP supplement is more important than the amount of RUP (Santos et al., 1998).

Since all the cows grazed the same pasture and similar amounts of ME were supplied by the respective concentrates, the cows on the three experimental treatments must have had a similar total ME supply in which case the ME must have been adequate for the higher level of production. Hence ME was not limiting for the cows on the control treatment indicating that another nutrient, such as CP, RUP or AA, could have been limiting, hence the response. The lack of response to the higher level of FM was probably because ME once again became the first limiting nutrient.

Apart from the effect of increased CP, the milk response of the cows on the two FM treatments over the control could be due to the increased supply of EAA, especially Lys and Met, to the small intestine. Santos et al. (1998) stated that FM consistently increased the proportion of Lys in the EAA flowing to the duodenum when supplied at greater than 4% of diet DM but not if less than 4%, and brought the ratio of Lys to Met, as % EAA, at the duodenum close to the recommended level. Xu et al. (1998) found increased milk production (39 vs. 34 kg/d) when cows were fed a blend of blood meal, FM and meat and bone meal as an AA source or ruminally protected Lys and Met compared to maize distillers grains as a control. Robinson et al. (1995) and Wu et al. (1997) also found increased milk yield with supplementation of ruminally stable Met and Lys while there have also been cases where responses were small and inconsistent (Rulquin et al., 1993). Supplementing FM (vs. solvent soyabean meal) increased milk yield and 3.5% FCM yield in the trial of Broderick (1992) where cows were fed lucerne silage. In the trial of MacDonald et al. (1998), where cows grazing pasture and receiving maize silage supplementation were supplemented with urea, SBM, or FM, the response was greater and more consistent for the cows receiving FM than SBM and there was no response to urea. The RUP supply was also greater from the FM than the SBM and zero from the urea, while the RDP supply was greatest from the SBM.

There is also a possibility that pasture intake was higher in the cows on the fish meal treatments, as predicted by the CPM Dairy model (Version 3.0.7a; Cornell University, Ithaca, NY, University of Pennsylvania, Philadelphia, PA; Willam H. Miner Agricultural Institute, Chazy, NY). This would have contributed to the higher milk production as well as being driven by the higher production since cows appear to consume feed to meet their energy demands (NRC, 2001). Some other studies also reported DMI and pasture intake for cows receiving RUP supplementation (Donaldson et al., 1991; Schor & Gagliostro, 2001) while other studies reported no difference in DMI (Santos et al., 1998; Bargo et al., 2003).

The response in milk fat and protein percentages may be partly due to the increased CP in the diet. In the study by McCormick et al. (2001a) milk fat (3.34 vs. 3.11%) and protein (3.42 vs. 3.27%) percentages were increased when Holstein cows grazing annual ryegrass-oat pastures were fed a high CP supplement (22.8% CP) vs. a moderate CP supplement (16.6% CP), while RUP sources (maize gluten meal-blood meal mixture) had no effect. The response could also be attributed to the increased flow of EAA to the small intestine as this is known to increase milk protein yield (Rulquin & Vérité, 1993). Supplementation with a protein source rich in EAA increases milk protein yield especially when maize (low in Lys) is fed and even with pasture of high N content (Rulquin & Vérité, 1993). Robinson et al. (1995) and Xu et al. (1998) found supplementing rumen protected Lys and Met to increase milk fat and protein percentages and yield. Increased milk protein concentration and yield have been the most consistent response to supplementing ruminally protected Met and Lys (Rulquin et al., 1993; Robinson et al., 1995; 1998; 1999). Supplementing FM (vs. solvent soyabean meal) increased milk protein percentage and yield in the trial of Broderick (1992). Some studies have shown no effect on milk fat (Robinson et al., 1999) or even a tendency to drop (Rulquin et al., 1993). Schor & Gagliostro (2001) found no effect of blood meal supplementation on milk fat concentration. Feeding FM could reduce milk fat percentage mainly due to high concentrations of unsaturated long-chain fatty acids in FM or a reduction in acetate : propionate ratio in ruminal fluid negatively affecting milk fat (Schroeder & Gagliostro, 2000). There was, however, no difference in ruminal acetate : propionate ratio between the control and high FM treatments in the present study (Table 5). The possibility that the Megalac could have contributed to the milk fat response cannot be ruled out.

The lactose response is in agreement with the results of Tesfa et al. (1995) with cows grazing a mixture of meadow fescue, timothy and red clover. The milk lactose was lower in cows supplemented with a cereal by-product based concentrate (12.4% CP) than in cows given additional N, in the form of urea or rapeseed meal (non-heat treated or heat treated), in the concentrates (15.0 to 15.6% CP). Robinson et al. (1995) found increased milk lactose when ruminally protected Lys and Met were fed. There is, however, no biological explanation as to why the lactose percentage should have increased.

There was no treatment effect on MUN (P > 0.10; Table 4). The values were within the range of 12 to 18 mg/dL, suggested by Linn & Olsen (1995) and De Villiers et al. (2000) as indicative of a balanced ration and still below 20 mg/dL where reproductive performance of the cow could start being negatively affected (De Villiers et al., 2000).

There was no effect on change in BW (P >0.10). The cows on the control treatment had a higher increase in BCS than the cows on the high FM treatment (P <0.05; Table 4). This could be because absorbed protein may induce mobilisation of body fat (Schor & Gagliostro, 2001). In the study of Schroeder & Gagliostro (2000) body fat mobilisation was possibly enhanced by RUP feeding. There was no difference between treatments in changes in BCS or BW in the study by Jones-Endsley et al. (1997) where the amount of CP in the concentrate was increased or in the study by Hongerholt & Muller (1998) where the RUP in the concentrate was increased.

The mean daily ruminal pH (Table 5) did not differ between the control and high FM treatments (P >0.10), as was expected since changing the level and source of protein did not affect ruminal pH in previous studies (Carruthers & Neil, 1997; Jones-Endsley et al., 1997; Bargo et al., 2001; 2003). Although the pH varied throughout the day, it was never below 5.8, the level at which cows start experiencing sub-clinical acidosis (Graf et al., 2005).

The mean daily ruminal NH3-N concentration was higher for the cows on the high FM treatment than the control (P <0.05), both well above the minimum level of 5 mg/dL for maximum microbial protein synthesis (Satter & Slyter, 1974) and within the range expected for cows on pasture-concentrate diets (Bargo et al., 2003). The higher ruminal NH₃-N concentration for the cows on the high FM treatment is to be expected due to the higher CP of the diet. Previous studies (Carruthers et al., 1997; Jones-Endsley et al., 1997; Bargo et al., 2001) reported higher NH₃-N concentrations when the concentrate contained more CP. The ruminal NH3-N, as well as the MUN, levels indicate that RDP was adequate, hence the deduction that the milk response may have been linked to RUP.

The VFA levels were in the expected range for cows on a pasture-concentrate feeding system (Kolver et al., 1998a; Schor & Gagliostro, 2001; Bargo et al., 2002a; 2002c; 2003). The concentration of total VFA in the ruminal fluid was higher for cows on the control treatment than the high FM treatment (P <0.05). There was no treatment effect on molar proportions (mol/100 mol total VFA) of acetate, propionate or butyrate or on the acetate : propionate ratio (P >0.10) although butyrate tended to be higher for the cows on the high FM treatment (P <0.10). The acetate concentration (81.5 and 75.4 mmol/L) was higher in the control cows (P <0.05). Differing the level and source of protein in the concentrate has been reported not to affect the total VFA or molar proportions of individual VFA (Bargo et al., 2001; Schor & Gagliostro, 2001).

These results indicate that cows grazing ryegrass and receiving maize and mineral supplementation respond in terms of milk yield and composition to up to 240 g FM a day, above which there is no additional response, indicating that energy might become the first limiting nutrient again.

In order for FM inclusion in the supplement to be profitable the additional revenue from the milk response would need to be greater than the additional feed cost. This was found to be the case during this trial illustrating that fish meal supplementation to cows on ryegrass can be profitable even though FM is expensive. The amount of additional profit made depends on the magnitude of the production response and the milk price.

 

Conclusions

High producing, multiparous Jersey cows in early to mid lactation grazing annual ryegrass pasture and receiving 6 kg as is (5.5 kg DM) a day of maize-based supplement, respond to the inclusion of FM in their supplement up to 240 g (as is) FM per day, above which there is no additional response. At this level of FM cows responded by producing 18% more FCM than control cows. This response can lead to increased profit. Additional protein needs to be included in the supplement, preferably of high quality (low degradability and good AA composition) to complement the highly degradable protein of the pasture. Future research could investigate other levels of FM, in the region of 240 g FM per day, to establish the optimal level. Further research should also be conducted using different breeds as well as different stages of lactation.

 

Acknowledgements

The authors would like to thank all the people who helped with the execution of the project including the staff of the Outeniqua Experimental Farm, George and the UP-Nutrilab, University of Pretoria, as well as the Western Cape Animal Production Research Trust and Western Cape Department of Agriculture for funding the project.

 

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