Comparison of a straw/concentrate mixture with silage as a buffer feed for grazing dairy cows

Over a 24-week period during the 1986 summer, three groups of January- to March-calving dairy cows were either grazed conventionally (G) or grazed between morning and afternoon milkings and housed overnight and offered grass silage (Si) or a straw/concentrate mixture (St) ad libitum. The straw/concentrate mixture contained proportionately, 0-33 long barley straw, 0·28 ground barley, 0·12 soya bean meal, 0·25 molaferm and 0·22 minerals. The metabolizable energy (ME) and crude protein (CP) contents of the silage fed in weeks 1-8 and weeks 9-24 were 9-5 and 10⁻⁶ MJ kg MD⁻¹ and 160 and 191 g kg DM⁻¹ respectively. The straw mix had an ME content of 10⁻¹ MJ kg DM⁻¹ and CP content of 134 g kg DM⁻¹. Partial storage feeding with silage or a straw/concentrate mixture led to a decrease in estimated herbage DM intake. The feeding of the straw/concentrate mixture increased total DM intake, but the estimated total ME intake was similar for treatments G and St. The intakes (kg DM d⁻¹) for treatments G, Si and St were respectively, herbage 11·7,6·8,4·1; total l3·5,13·6,15·0; total ME intake (MJd⁻¹) 163, 155, 163.
Animal performance was, for treatments G, Si and St respectively: milk yield (kg d⁻¹) 19·2, 17·5, 19·1 (s.e.d. 0-87); milk fat content (g kg⁻¹) 36·9, 37·6, 37.1 (s.e.d. 1.22); milk protein content (g kg⁻¹) 35·3, 32·9, 33·4 (s.e.d. 0·76).     

Supplementary feeding of forage to grazing dairy cows

For three 8-week periods of the grazing season 48 spring-calving cows were continuously stocked at either a high or a low rate (average 4.9 and 4.3 cows ha⁻¹ respectively) which declined through the season. Within each stocking rate group half the cows were allowed access to hay for 45 min after morning milking; the other half received no hay.
Total dry matter (DM) intakes were increased by offering hay, and intakes of hay were greater at the high stocking rate and during prolonged periods of inclement weather. However, there were times when, because of low herbage height and adverse weather, offering hay once daily could not prevent a decline in total DM intake. Grazing time was reduced and ruminating time increased by offering hay, but the rate of biting at pasture was unaffected. Hay DM was eaten at twice the rate of intake of herbage DM.
Offering hay increased milk yield in early season and liveweight gain in late season. The benefits of offering hay were greatest for the higher yielding cows. There were no significant effects on milk composition.
Stocking rate had only small effects on herbage height, but stocking at the higher rate tended to reduce herbage DM intake and reduced live-weight gain in late season. Levels of utilized metabolizable energy from grazed herbage were high (average 106 GJ ha⁻¹) but were reduced by feeding hay and stocking at the lower rate.     

The effect of offering a brewers grains/treated straw supplement to grazing dairy cows

In a two-year study, set stocked dairy cows were offered a mixture of brewers grains and sodium hydroxide-treated straw (1:1 on a dry matter basis)for 1 h daily. The experiments lasted for 20 and 19 weeks, mean supplementary (buffer) feed dry matter intakes were 3·0 and 3·4 kg d^-1 and mean sward heights (rising plate meter) were 4·9 and 4·7 cm in 1988 and 1989 respectively. The control group received no supplementation. The buffer feed significantly increased milk yield (26·3 vs 24·6 kg d^-1 and 28·6 vs 26·3kg d^-1 in 1988 and 1989 respectively), increased liveweight gain (0·27 vs 0·13 kg d^-1 and 0·27 vs 0·17 kg d^-1) and increased effective stocking rate (5·17 vs 4·69 cows ha^-1and 5·10 vs 4·53 cows ha^-1). There were no significant effects on milk composition. The greatest responses in milk production were found in the late grazing season.     

The effect of two contrasting concentrate allocation strategies on the performance of grazing dairy cows

The objective of this study was to examine the performance of grazing Holstein–Friesian dairy cows when equal quantities of concentrates were offered using either a flat‐rate or a feed‐to‐yield allocation strategy. The study involved fifty‐six cows (twenty primiparous and thirty‐six multiparous) and continued for 122 d, with concentrate feed levels adjusted on five occasions during the study (every four weeks approximately). Total concentrate intake over the duration of the study was 463 and 525 kg cow^?1 (3·8 and 4·3 kg cow^?1 d^?1) for multiparous and primiparous animals respectively. Concentrate allocation strategy had no effect on average daily milk yield, milk fat or protein content, milk‐fat‐plus‐protein yield or end‐of‐study live weight and body condition score (P > 0·05). In conclusion, concentrate allocation strategy had minimal impact on the overall performance of these mid/late lactation cows when concentrate feed levels were modest and grass availability was high.     

Effects of post‐grazing herbage height and concentrate feeding on milk production and major milk fatty acids of dairy cows in mid‐lactation

Milk fatty acids (FA) were compared in mid‐lactation dairy cows in four feeding systems combining grazing management and supplementation. The four treatments were factorial combinations of compressed herbage grazed to 3·7 or 4·6 cm post‐grazing height, with or without concentrate feeding (3·6 kg cow^?1 d^?1). Milk yield and composition were measured for four groups of eight Friesian × Jersey dairy cows over 3 weeks in mid‐lactation for cows that had grazed treatments for 64 d from early spring. Milk yield was higher in cows fed concentrate plus herbage (23·9 kg d^?1 cow^?1) than cows fed herbage only (20·3 kg d^?1 cow^?1). Milk fat percentage was higher in cows fed herbage only (5·5%) than that fed herbage plus concentrate (5·1%). Milk protein percentage was higher in cows fed herbage plus concentrate (4·0%) than that fed herbage only (3·7%). The concentrations of conjugated linoleic acids c9, t11, C18:0, C18:1 t11 and C18:2 t9, c12 FA were lower where concentrate was fed. The concentrations of C18:1 t10, C18:1 t5, t8 and C18:2 c9, c12 FA were higher where concentrate was fed. The concentrations of C18:1 c6, C18:1 c9, C18:1 t9 and C18:3 c6,9,15 were unaffected by concentrate feeding. Post‐grazing herbage height had no significant effect on milk yield or concentration of milk FA. Provided dairy cows are harvesting leafy material of similar nutrient and FA concentration, post‐grazing herbage height does not appear to alter milk FA and the supply of high energy concentrates is more influential on milk FA profiles.     

The effects of offering a range of forage and concentrate supplements on milk production and dry matter intake of grazing dairy cows

An experiment was undertaken to examine the effect of supplement type on herbage intake, total dry matter (DM) intake, animal performance and nitrogen utilization with grazing dairy cows. Twenty‐four spring‐calving dairy cows were allocated to one of six treatments in a partially balanced changeover design with five periods of four weeks. The six treatments were no supplement (NONE), or supplementation with either grass silage (GS), whole‐crop wheat silage (WS), maize silage (MS), rapidly degradable concentrate (RC) or slowly degradable concentrate (SC). Cows were rotationally grazed with a mean herbage allowance of 20·5 kg DM per cow per day, measured above 4 cm. Forage supplements were offered for approximately 2 h immediately after each morning milking, with cows on NONE, RC and SC treatments returning to the grazing paddock immediately after milking. Cows on treatment MS had a significantly higher supplement DM intake than the other treatments but a significantly lower grass DM intake than the other treatments, resulting in no significant difference in total DM intake when compared with cows on treatments WS, RC and SC. Concentrate type had no significant effect on herbage intake, milk yield, milk composition or yield of milk components. The yield of milk fat and milk protein was significantly higher on treatments MS, RC and SC compared with treatments NONE, GS and WS. The results indicate that despite a relatively high substitution rate, maize silage can be a useful supplement for the grazing dairy cow.     

Concentrate supplementation of grazing dairy cows. 2. Effect of concentrate composition on herbage intake and milk production

The effect of feeding either traditional concentrates containing starch or high quality fibrous concentrates on the performance of grazing dairy cows was examined in a trial in which cows were given concentrates with either 350 g starch and sugars (kg dry matter (DM))^-1 (high-starch) or 100 g starch and sugars (kg DM)^-1 (high-fibre). The swards used consisted predominantly of perennial ryegrass and were usually aftermaths following cutting. Each area was grazed for 3 or 4 d at each grazing and a two-machine sward-cutting technique was used for estimating herbage intake.
The effect of concentrate composition on the herbage intake of grazing cows at a high daily herbage allowance of 28 kg OM above 4 cm cutting height was investigated in 1983 and 1984. With 54 kg OM d^-1 of high-starch concentrates the mean herbage intake was 11·5 kg OM d^-1 per cow while cows fed 5.3 kg d^-1 of high-fibre concentrates consumed on average 12–6 kg OM d^-1. The mean substitution rate of herbage by concentrates was reduced from 0·45 kg herbage OM (kg concentrate OM)^-1 with the high-starch concentrate to 0·21 with the high-fibre concentrates.
The effect of the treatments on milk production was studied in 1984. The cows consumed 5·5 kg OM d^-1 as concentrates and grazed at a lower herbage allowance of 19 kg OM above 4 cm cutting height. With high-fibre concentrates milk production and 4% fat-corrected milk production were 13 and 1·8 kg d^-1, respectively, higher than with the high-starch treatment. The daily live weight gain with the high-starch concentrates was 0·17 kg per cow more than with the high-fibre concentrates.     

Continuous and rotational grazing of dairy cows – the interactions of grazing system with level of milk yield, sward height and concentrate level

An experiment was conducted to test the hypothesis that for cows with high levels of milk yield, rotational grazing produces higher milk yields than continuous grazing. The comparison of grazing systems was made at two levels of milk yield (initially 20·3 and 32·5 kg d^?1), and interactions with sward height and concentrate level were also examined. The study used 48 multiparous Holstein Friesian cows over a period of 62 d. Mean milk yield, its persistency and composition, live weight, body condition score and liveweight gain were not significantly affected by grazing system at either level of milk yield. There were no significant interactions between grazing system and sward height or concentrate level for any milk production measurement. Mean estimated herbage and total dry matter (DM) intake (P < 0·01), grazing time (P < 0·05) and ruminating time (P < 0·01) were significantly greater on the continuous grazing system. The cows in the higher milk yield group and those grazed at the higher sward height had a significantly (P < 0·05) higher estimated daily herbage DM intake and rate of herbage intake on the continuous grazing system than those on the rotational grazing system. There was no evidence to support the hypothesis that rotational grazing systems support higher levels of milk production than continuous grazing for cows of high milk yield. The shorter grazing time on the rotational grazing system indicated that cows may anticipate the timing of the daily movement of the electric fence, and this reduces their time spent grazing residual herbage.     

The effects of a flexible grazing management strategy and leader/follower grazing on the milk production of grazing dairy cows and on sward characteristics

An experiment was carried out during 1984 to examine the effects of three alternative grazing strategies for January/February calved British Friesian dairy eows on sward and animal production. Cows were rotationally grazed across 1 d paddocks without concentrate supplementation from 30 April to 1 October. A flexible grazing (EG) treatment involved manipulating residual herbage height, as assessed by a rising-plate sward stick, with cows initially grazing to 80 mm, reducing to 60 mm when milk yield declined below 20 kg d^?1 and finally to 50 mm when milk yield declined below 15 kgd^?1. Control (C) cows grazed to a constant residual herbage height of 60 mm throughout the season (a 60-inm rising-plate sward stick height is equivalent to a sward surface height of approximately 80 mm). On a further treatment a leader/follower (LF) approach was used, with cows paired for calving date and parity and within pairs allocated to either a high-(leader) or a low-yielding (follower) group, according to milk yield at turnout, with the leader group grazing 1 d ahead of the follower group. Overall stocking rates on C and LE treatments were identical but herbage allowances differed as a result of treatment effects. Animal performance data for the FG, C and LE treatments, respectively, were: milk yield (kg d^?1) 14·5, 14·7 and 16·0 (s.e. 0·59); milk fat yield (g d^?1) 577, 571 and 637 (s.e. 29); milk protein yield (g d^?1) 528, 527 and 576 (s.e. 19); and liveweight gain (kg d^?1) 0·09, 0·20 and 0·14 (s.e. 0·04). Overall, there was no benefit in animal production following lax grazing in spring even with high-yielding cows, and this approach resulted in the accumulation of stem and senescent material in the sward in mid-season. However, preferential treatment of high-yielding cows by grazing as a leader group in a leader-follower system resulted in higher milk production, particularly in late season, with an overall improvement in milk yield for the LF treatment of 9% relative to treatment C.     

A simulation model of a dairy forage system to evaluate feeding management strategies with spring rotational grazing

Abstract To counteract a decrease in the availability of grazing for feeding dairy cows in France, a simulation model is proposed in the paper, which combines decision and agronomic submodels to study forage system management strategies compatible with spring grazing use. Nine strategies were tested with the model using a sequence of 16 climatic years. Three of these strategies come from a survey in south‐west France and six others were designed with research scientists or farm advisors. The strategies differ in the duration of maize silage feeding, the area dedicated to maize silage and the area dedicated to grass silage. Results from simulation models show that the consequence of a large and constant maize silage area is a high maize silage overstock if there is an early turnout or a high grass silage overstock if turnout is late. The consequence of a low maize area is a high grazing duration combined in some years with feeding shortages. Strategies that have no feeding shortage and a low level of maize and grass silage overstock have a high grazing duration and have no constant maize or grass silage areas. The solution proposed to avoid climatic risk, and its consequences on feeding, is based on two procedures: use of reserve areas for production and allowing the production programme to be modified to take into account fresh information, especially weather records.     

The use of conserved forage as a supplement for grazing dairy cows

The difficulty in matching the herbage requirements of grazing dairy cows to herbage production, due mainly to the unpredictability of the latter., causes stocking rates to be too low for maximum per hectare production and, thus, cows to be underfed at certain times in the grazing season. Conserved forage may be used as a supplement for grazing dairy cows in order to reduce variation in forage intake by the cow, to allow pasture stocking rates to be increased and to increase the efficiency of land use. The effect of offering conserved forage with herbage on intakes and production is reviewed in comparison to both ad libitum and restricted herbage. Total nutrient intakes and milk fat + protein yields are reduced for cows offered herbage and supplementary forage compared with cows offered ad libitum herbage, but increased compared with cows offered a restricted herbage level. Increasing pasture stocking rates may allow increases in utilized metabolizable energy levels from grassland but further research is needed in this area. Both grass and maize silage supplements offer potential for increasing the efficiency of land use, but in the case of grass silage this is only achieved in the best management practices.     

A comparison between supplements to silage of high digestibility offered to dairy cows

Grass silage containing 180 g crude protein and 660g digestible organic matter per kg DM was offered to forty-two dairy cows for 20 weeks in a self-feeding system. In addition, supplements of either mineralized barley (130 g crude protein per kg DM) or barley plus groundnut (180 g crude protein per kg DM) were offered. The mean daily milk yields were 18·5 and 19·4 kg per cow respectively.     

A comparison of grass/white clover and grass silages offered to dairy cows as the sole feed

Two diets were compared: perennial ryegrass ( Lolium perenne L.) silage and perennial ryegrass/white clover ( Trifolium repens L.) silage, in each case fed ad libitum , without supplementation, to lactating dairy cows. The comparison was made with silages cut on each of four dates. The crops were wilted to a dry matter content of at least 256g kg^-1 and no additives were used.
The grass/clover silages were well preserved at all four cuts. The grass was well preserved at three cuts, but, at a May cut, the grass silage was less well preserved and less digestible than the grass/clover silage. When the May silages were fed, milk yield was higher with grass/clover than with grass. Taking the experiment as a whole, however, milk yield and composition were similar on the two diets. The grass/clover silages had a lower proportion of cell wall and their intake by dairy cows was consistently higher than that of the grass silages.
It is concluded that perennial ryegrass/white clover crops can be ensiled successfully and fed successfully, with high intake, to lactating dairy cows, but it should not be assumed that cows will give more milk than when fed equivalent all-grass silage.     

Supplementary feeding of forage to grazing dairy cows, 3. The effect of three daytime stocking rates on the performance of cows offered grass silage overnight

Over a 24-week period, three groups of dairy cows were continuously stocked at 8, 10 or 12 cows ha^-1 between morning and afternoon milkings, and overnight were housed and offered grass silage ad libitum. Due to a prolonged drought, sward heights only averaged 4·1 cm.
The increase in daytime stocking rate led to a decline in herbage intake, and increases in silage intake. At the highest stocking rate (12 cows ha^-1), the silage intake failed to compensate for the reduced herbage intake. Consequently the total dry matter and estimated metabolizable energy intakes were lower than for the 8 and 10 cows ha^-1 treatments. Milk yields and milk composition were not significantly affected by treatment but the 12 cows ha^-1 stocking rate gave the lowest milk and milk solids yields.
The utilized metabolizable energy (UME) on the grazed swards was greatest for the 10 cows ha^-1 treatment. The sward cut to provide the silage had a UME level (GJ ha^-1) 32% greater on average than the grazed swards during the same growth period. The total areas utilized for grazing and silage production for 8, 10 and 12 cows ha^-1 were 0·240, 0·224 and 0·215 ha respectively. Fat and protein yields per unit area were greatest for the 10 cows ha^-1 group.     

Milk yield and nitrogen excretion of dairy cows grazing binary and multispecies pastures

Three grazing experiments were carried out in late spring (early lactation), summer (mid‐lactation) and autumn (late lactation) to compare the effects of perennial ryegrass cultivar or grass species, sown in binary or multispecies mixtures, on milk yield and nitrogen excretion of dairy cows. Replicated groups of multiparous Holstein Friesian × Jersey cows were offered either a control or high‐sugar perennial ryegrass (Lolium perenne) or tall fescue (Festuca arundinacea) base grass in a binary mixture with white clover (Trifolium repens) or in a multispecies mixture with additional legumes, bromegrass (Bromus willdenowii) and forbs. During each 9‐day experiment, botanical composition, milk production and faecal and urine composition were measured. Milk solid (MS) yield for the control ryegrass, high‐sugar ryegrass and tall fescue grass types averaged, respectively, 1.53, 1.64 and 1.70 kg MS cow^?1 day^?1 for a binary mixture sward, compared with 1.65, 1.54 and 1.53 kg MS cow^?1 day^?1 for a multispecies sward. Legume content influenced milk production more than the number of species present in a mixture. There was lower urine N concentration from a multispecies sward compared with a binary mixture. Urine N concentration of cows grazing the control ryegrass, high‐sugar ryegrass and tall fescue grass types averaged, respectively, 4.6, 5.3 and 6.8 g N L^?1 for a binary mixture, compared with 4.1, 3.9 and 3.9 g N L^?1 for a multispecies mixture. Feeding dairy cows on multispecies swards containing forbs presents an opportunity to reduce N losses without compromising milk yield.     

Herbage intake and milk production by grazing dairy cows 2. The effects of level of winter feeding and daily herbage allowance

Two experiments are described in which two levels of winter feeding and three levels of herbage allowance during the grazing season were imposed upon March/April calving British Friesian dairy cows. The winter treatments resulted in differences in live weight and milk yield at turnout of 35 and 53 kg and 3·4 and 3·2 kg d^-1 for the two trials. Subsequently, when grazed at generous herbage allowances, the cows were able to compensate for much of this difference but when herbage was restricted the milk yield differences were accentuated. Groups of cows from each winter treatment were offered 25, 50 or 75 (Experiment 1) and 30, 50 or 70 (Experiment 2) g herbage DM per kg LW daily during the grazing season. Daily herbage intakes on the three allowances in each trial were 14·1, 13·3, 10·7 and 12·5, 12·1, 11·5 kg OM and milk yields were 16·0, 15·3, 12·5 and 15·2, 14·3, 11·8 kg SCM respectively. Both intake and milk production were depressed once the cows were forced to consume more than 50% of herbage on offer or to graze the sward down to a mean height of less than 8–10 cm. Grazing behaviour observations indicated that under rotational managements the cows did not compensate for restrictions in available herbage by grazing longer. Highest levels of milk production per unit area were observed in both trials when production per cow was depressed by 20–25%.     

The effects of feeding fodder beet to dairy cows offered silage ad libitum

In a 16-week winter feeding experiment, 48 autumn calving cows and heifers were used to compare a control diet, with two diets including fodder beet at a low and a high level. The control diet was ad libitum silage and 6 kg d^-1 of concentrates (13.4 MJ (kg DM)^-1 of ME and 197 g (kg DM)^-1 of CP). The cows offered fodder beet were fed the control diet (C) plus fodder beet at either 2 (L) or 4 (H) kg DM d^-1. Soya bean meal was offered with the fodder beet at 0.5 or 1.0 kg d^-1 for diets L and H, respectively.
Total dry matter and metabolizable energy intakes were 15.2,16.4 and 17.3 kg DM d^-1; 177, 195 and 211 MJ d^-1 for treatments C, L and H, respectively. The mean milk yields were not significantly affected by the feeding of fodder beet. There was a significant improvement in the fat and protein content of the milk and yield of constituents. The milk composition and yield of solids were: fat content 42.3,44.2 and 45.9 (s.e.d. 1.25) g kg^-1; protein content 33.0, 34.5, 35.3 (s.e.d. 0.76) g kg^-1; fat yield 964,1027,1095(s.e.d. 63.2); protein yield 757, 801, 841 (s.e.d. 48.8) for treatments C, L and H, respectively. The treatments had no significant effect on live weight or condition score change.     

The use of n-alkanes to estimate herbage intake and diet composition by dairy cows offered a perennial ryegrass/white clover mixture

The n-alkane technique for estimating herbage intake and diet selection in dairy cows fed perennial ryegrass (Lolium perenne)/white clover (Trifolium repens) herbages was evaluated. Pairs of animals were offered either 8, 10, 12 or 14 kg dry matter (DM) d^?1 of herbage alone or with 2 kg DM d^?1 of barley. Fresh herbage was cut daily from a perennial ryegrass/white clover sward and the appropriate amount was fed in four feeds during the day. Individual intakes and the white clover proportion of the diet were estimated during a 12-d period using the n-alkane technique. Animals were dosed twice daily with paper pellets containing dotriacontane (C₃₂-alkane). Faecal grab samples were collected after the morning and afternoon milking. Three least-squares optimization methods were compared in calculating the white clover proportion in the diet; then, total DM intake was calculated. The different least-squares optimization methods gave similar predictions of the white clover content of the forage consumed. No significant (P < 0.05) effects of sampling routine, concentrate (barley) fed or interactions between the two were detected with respect to the difference between calculated and actual intake, the difference as a proportion of the total intake and estimated white clover content of the diet. The difference between the calculated and actual intake ranged from 139 to 366 g DM d ^?1, which resulted in a proportional difference ranging from 0.004 to 0.02 depending on sampling routine. The actual white clover content of the herbage mixture fed was 0.42 ± 0.008, whereas the estimated white clover content ranged from 0.41 ± 0.006 to 0.43 ± 0.008. The results suggest that accurate herbage intake estimates can be achieved in dairy cows grazing perennial ryegrass/white clover swards if representative samples from herbage consumed can be collected.     

Quantifying the influence of sward height, concentrate level and initial milk yield on the milk production and grazing behaviour of continuously stocked dairy cows

Two factorial design experiments were carried out in the spring of 1994 and 1995, each of 6 weeks, to quantify the effects of sward height (SH), concentrate level (CL) and initial milk yield (IMY) on milk production and grazing behaviour of continuously stocked dairy cows. In Experiment 1, forty‐five Holstein Friesian cows were in five groups with initial milk yields of 16·9, 21·1, 28·0, 31·5 and 35·5 kg d^–1, grazed sward heights were 3–5, 5–7 and 7–9 cm (LSH, MSH and HSH respectively), and concentrates were fed at rates of 0, 3 and 6 kg d^–1. In Experiment 2, 48 cows were in two groups with IMY of 21·3 and 35·5 kg d^–1, grazed sward heights were 3–5 and 7–9 cm (LSH and HSH), and concentrates were fed at 0 and 6 kg d^–1 and ad libitum. Multiple regression models were used to quantify the effects of the three variables on milk yield persistency (MYP), estimated herbage dry‐matter (DM) intake (HDMI), grazing time (GT) and rate of DM intake (RI). The partial regression coefficients showed that increased SH led to increased MYP (Experiment 1 P < 0·001, Experiment 2 P < 0·05), increased HDMI (P < 0·01, P < 0·01), increased GT (P < 0·001, P < 0·05) and increased RI (P < 0·001, P < 0·05). Increasing CL led to increased MYP (NS, P < 0·001), decreased HDMI (P < 0·001, P < 0·001), decreased GT (NS, P < 0·001) and decreased RI (P < 0·001, P < 0·001). Higher IMY level of cows decreased MYP (P < 0·001, P < 0·001), increased HDMI (P < 0·001, P < 0·001), increased GT (P < 0·001, P < 0·05) and increased RI (P < 0·05, P < 0·01). The models were highly significant (P < 0·001), and accounted for 0·48–0·87 of the total variance. The partial regression coefficients quantified the extent to which GT and RI by cows respond positively to higher IMY, and negatively to increased CL, but respond differently (GT declines in response to a higher RI) with increasing SH.