Remy Delagarde

Effect of the level of concentrate supplementation, herbage allowance and milk yield at turn-out on the performance of dairy cows in mid lactation at grazing

In order to establish the response of dairy cow performance to concentrate supplementation in contrasting grazing conditions and for cows differing in milk yield at turn-out, three experiments were conducted. Each year, two levels of herbage allowance were studied in interaction with four (experiment 1) or three (experiments 2 and 3) levels of concentrate on two groups of 30 to 40 mid-lactation Holstein cows producing between 20 and 46 kg milk at turnout. Amount of concentrate and herbage allowance ranged from 0 to 6 kg fresh weight and from 12 to 22 kg dry matter (DM) per cow per day respectively. The supplementation led to average responses, per kg DM concentrate, of 104 kg milk, +66 g/day body-weight gain, +0·19 g/kg milk protein and -0·57 g/kg milk fat. These responses remained linear up to 4 or 6 kg according to the years and treatments. The response to the concentrate did not vary with the milk yield or composition at turn-out. The increase in the herbage allowance from 12 to 16 kg DM per cow per day (experiment 1) improved milk yield (+1·2 kg/day) and milk protein (+0·7 g/kg) while the increase from 16 to 22 kg DM (experiments 2 and 3) had less effect (+0·5 kg/day milk yield and +0·4 g/kg milk protein). There was no clear interaction between concentrate supplementation and herbage allowance. Under the usual conditions of spring pasture, with cows in mid lactation, the use of a constant level of concentrate at grazing proves to be a technique of some interest.

INCLUSION OF WHITE CLOVER IN STRIP-GRAZED PERENNIAL RYEGRASS SWARDS: HERBAGE INTAKE AND MILK YIELD OF DAIRY COWS AT DIFFERENT AGE OF SWARD REGROWTH

The introduction of legumes in grass-based swards provides some economic and agronomic advantages, often allowing an increase in the performance of grazing ruminants. The aim of this study was to obtain a better quantification of the nutritional benefits to dairy cows after introducing white clover into swards of perennial ryegrass (PRG), using two ages of regrowth. Four treatments were studied in a 2 ✕ 2 factorial design with two sward types and two ages of regrowth. The swards were either a pure perennial ryegrass sward with nitrogen (N) fertilization, or a perennial ryegrass/white clover mixture (GC) with no N fertilization. The regrowth ages were 19 and 35 days (treatments: PRG19, PRG35, GC19 and GC35). The proportion of clover in the GC swards was on average 420 g/kg dry matter (DM). Twelve late-lactation Holstein cows, fistulated at the rumen and duodenum, were used according to a 4 ✕ 4 Latin-square design with four 11-day periods. The pasture was strip-grazed with 12 kg DM per cow of herbage above 5 cm offered daily in all the treatments. The effects of sward type and regrowth age were often additive, in particular for herbage intake and milk yield. Herbage organic matter (OM) intake, duodenal non-ammonia N (NAN) flow and milk yields were higher on the GC swards and lower on the older regrowths. Finally, the performance of the cows was similar on the PRG19 and GC35 treatments. The OM digestibility of the selected herbage as well as the duodenal nitrogen flux per kg digestible OM intake was not affected by the sward type. Ruminal fermentations were more intense with mixed swards and the youngest regrowths. The daily grazing time and the daily pattern of grazing activities were modified by the type of sward and by regrowth age. The average OM intake rate was higher on the GC swards than on the PRG swards. In this study, the nutritional advantage of introducing white clover into swards of perennial ryegrass was related to an increase in herbage intake and not to any improvement in the nutritive value of the sward.

The effect of nitrogen fertilization level and protein supplementation on herbage intake, feeding behaviour and digestion in grazing dairy cows

An experiment is described to study the influence of nitrogen (N) fertilization and protein supplementation on the nutrition of grazing dairy cows. Two levels of N fertilization (0 and 60 kg N per ha per regrowth) and two levels of soyabean meal supplementation (0 and 2 kg day−1) were factorially combined and compared in a 4 × 4 Latin square design using periods of 11 days. Eight fistulated Holstein cows were strip grazed on perennial ryegrass pastures at a constant daily herbage allowance — measured above 5 cm from ground level — of 20 kg OM cow−1. The individual herbage OM intake was calculated using chromic oxide and faecal N and ADF contents. Grazing behaviour, duodenal digesta flow and ruminal fermentation patterns were also measured. No interaction was found between fertilization and supplementation levels. Herbage OM intake was greatly depressed in unfertilized swards (−2.0 kg OM day−1). This could be attributed to a decrease of the rate of intake due to the lower green leaf mass (1.6 vs. 2.3 t OM ha−1). Herbage OM digestibility, non-ammoniacal N (NAN) flow into the duodenum and ruminal fermentations were reduced on unfertilized swards. However, the sites of OM digestion and NAN flow expressed g per kg digestible OM intake were similar at both fertilization levels. Cows receiving protein supplementation showed similar herbage intake, but higher total OM intake and NAN flow than unsupplemented cows. The low level of concentrate fed, and perhaps also its composition, may explain the additivity between herbage and concentrate. Treatments had no effect on total grazing time nor on mean rate of biting.

Managing variations in dairy cow nutrient supply under grazing.

Grazed pasture, which is the cheapest source of nutrients for dairy cows, should form the basis of profitable and low-input animal production systems. Management of high-producing dairy cows at pasture is thus a major challenge in most countries. The objective of the present paper is to review the factors that can affect nutrient supply for grazing dairy cows in order to point out areas with scope for improvement on managing variations in nutrient supply to achieve high animal performance while maintaining efficient pasture utilisation per hectare (ha). Reviewing the range in animal requirements, intake capacity and pasture nutritive values shows that high-producing cows cannot satisfy their energy requirements from grazing alone and favourable to unfavourable situations for grazing dairy cows may be classified according to pasture quality and availability. Predictive models also enable calculation of supplementation levels required to meet energy requirements in all situations. Solutions to maintain acceptable level of production per cow and high output per ha are discussed. Strategies of concentrate supplementation and increasing use of legumes in mixed swards are the most promising. It is concluded that although high-producing cow cannot express their potential milk production at grazing, there is scope to improve animal performance at grazing given recent developments in our understanding of factors influencing forage intake and digestion of grazed forages.

Herbage intake and behavioural adaptation of grazing dairy cows by restricting time at pasture under two feeding regimes.

The time at pasture of dairy cows is often restricted in the context of extending the grazing season in autumn or at the end of winter. The objective of our study was to evaluate the effects of a restriction of time at pasture on milk production, herbage intake and feeding behaviour in dairy cows according to feeding regime. The four treatments consisted of 4 h or 8 h of time at pasture per day tested under two feeding regimes combining rate of supplementation and herbage allowance: either a high rate of supplementation (10 kg dry matter (DM) of a maize silage-soya bean meal mixture in the ratio 87 : 13 on a % DM basis) with a low herbage allowance (6 kg DM/cow per day above 5 cm), or a low rate of supplementation (5 kg DM of the same supplement) with a high herbage allowance (11 kg DM/cow per day). The study was carried out according to a 4 × 4 Latin square design with four 2-week periods, with 48 mid-lactation Holstein cows. The cows in the 4-h treatment had access to pasture from 0900 h to 1300 h and those in the 8-h treatment from 0900 h to 1700 h. The supplement was given at 1830 h. When time at pasture was reduced from 8 h to 4 h per day, herbage intake decreased (9.9 v. 8.1 kg DM, P < 0.001), along with a fall in milk production (22.3 v. 21.2 kg, P < 0.001) and milk protein concentration (30.1 v. 29.6 g/kg, P < 0.001), while milk fat concentration increased (39.4 v. 39.9 g/kg, P < 0.05). The effect of time at pasture on milk production was slightly more marked on the low-supplement feeding regime (interaction P < 0.06). Reducing time at pasture by 4 h led to a sharp decrease in grazing time (327 v. 209 min, P < 0.001), but strongly increased the pasture intake rate (31 v. 39 g DM/min, P < 0.001) and the proportion of time spent grazing (0.68 v. 0.87, P < 0.001). Cows showed a stronger motivation for grazing when receiving the low-supplement feeding regime. In conclusion, we showed that reducing time at pasture from 8 to 4 h for cows receiving 5 to 10 kg DM of a maize silage-based supplement decreased moderately milk production and herbage intake, because of the capacity for behavioural adaptation by the grazing dairy cows.

N-alkanes v. ytterbium/faecal index as two methods for estimating herbage intake of dairy cows fed on diets differing in the herbage:maize silage ratio and feeding level

The aim of this study was to compare the n-alkanes and the ytterbium (Yb)/faecal index techniques as two methods for estimating the herbage intake of dairy cows fed indoors on different herbage : supplement ratios and feeding levels. The supplement was a mixture of maize silage and soyabean meal (ratio of 87 : 13 on a dry matter (DM) basis). In all, four treatments were studied. The herbage : supplement ratio in the diet was 25 : 75, 50 : 50, 75 : 25 and 50 : 50 for treatments 1, 2, 3 and 4, respectively. Animals were offered for treatments 1, 2 and 3, 100% of ad libitum intake measured before the experiment and 70% of ad libitum intake for treatment 4. Cows were fed herbage in the morning and supplement in the evening. A total of six lactating Holstein dairy cows were used in a 4 × 4 Latin square with four 14-day periods. Herbage and supplement intakes, faecal output (FO), in vivo organic matter (OM) digestibility and faecal recovery of markers were measured on the last 5 days of each period. Intake was estimated with the two methods and from two faecal sampling techniques, that is, total faecal collection v. grab sampling during milking. Mean herbage intake as fed, or estimated from n-alkanes or from the Yb/faecal index was 7.7, 8.1 and 10.2 kg DM, respectively. The mean prediction error, expressed as a fraction of actual herbage intake, was 0.10 and 0.50 for the n-alkanes and Yb/faecal index methods, respectively. The n-alkanes method clearly showed much better accuracy than the Yb/faecal index method for estimating intake, irrespective of the faecal sampling method, herbage : silage proportion or feeding level. For the n-alkanes method, herbage intake was slightly overestimated (7%) when herbage proportion in the diet was high, due to a ratio of faecal C33 : C32 recovery >1. The high bias for the Yb/faecal index was due to the cumulative effect of overestimation of FO (mean recovery of Yb = 0.92) and underestimation of the diet indigestible fraction (-8%). Between-treatment variations of FO were on average well estimated by Yb. Between-treatment variations of OM digestibility estimated using the faecal index technique were lower than those observed in vivo. It is concluded that intake of grazing dairy cows receiving high levels of maize silage supplement should be estimated using the n-alkanes method.

Comparison of intake and digestibility of fresh Digitaria decumbens grass fed to sheep, indoors or at pasture, at two different stages of regrowth

The effect of two feeding systems (indoors and at pasture) on intake and digestion of fresh grass was studied at two stages of regrowth (21 and 35 days of regrowth) in two parallel experiments. In Experiment 1, 10 adult Martinik rams weighing, on average, 50.5 (± 0.9) kg, including four fitted with rumen cannula, were randomly allocated to two groups according to a 2 × 2 Latin Square design. These rams consumed a 21-day regrowth of Digitaria decumbens grass diet during two successive 28-day periods, indoors (five rams) or at pasture (five tethered rams). In Experiment 2, 10 other Martinik rams weighing, on average, 45.5 (± 0.9) kg, including four fitted with rumen cannula, were randomly allocated to two groups according to a 2 × 2 Latin Square design. These rams consumed a 35-day regrowth of D. decumbens grass diet during two successive 28-day periods, either indoors (five rams) or at pasture (five tethered rams). For the indoors groups, in vivo organic matter digestibility (OMD) was measured by total collection of feces. In addition, OMD was estimated indoors and at pasture using the fecal CP (CPf) method (OMDCPf). Organic matter intake (OMI) was then estimated using OMDCPf and fecal organic matter output (OMICPf). Correlations of 0.49 and 0.77 were found between in vivo OMD and OMDCPf (P < 0.05) and between OMI and OMICPf (P < 0.001), respectively. OMDCPf was 1.8% (P < 0.05) and 2.7% (P < 0.01) lower indoors than at pasture at 21 and 35 days of regrowth, respectively, whereas OMICPf indoors was 1.1 and 1.16 times that registered at pasture at 21 and 35 days of regrowth, respectively. The higher OMDCPf at pasture was linked to the higher selective behavior of rams at pasture, whereas the differences in OMICPf between the two feeding systems were linked to differences in the total bulk density of the grass. These studies show that differences in OMDCPf and OMICPf exist between animals fed indoors and at pasture with the same forage and that these differences may vary according to the stage of regrowth of the grass offered.

Pasture intake and milk production of dairy cows rotationally grazing on multi-species swards.

Increasing plant species diversity has been proposed as a means for enhancing annual pasture productivity and decreasing seasonal variability of pasture production facing more frequent drought scenarios due to climate change. Few studies have examined how botanical complexity of sown swards affects cow performance. A 2-year experiment was conducted to determine how sward botanical complexity, from a monoculture of ryegrass to multi-species swards (MSS) (grasses-legumes-forb), affect pasture chemical composition and nutritive value, pasture dry matter (DM) intake, milk production and milk solids production of grazing dairy cows. Five sward species: perennial ryegrass (L as Lolium), white clover and red clover (both referred to as T as Trifolium because they were always sown together), chicory (C as Cichorium) and tall fescue (F as Festuca) were assigned to four grazing treatments by combining one (L), three (LT), four (LTC) or five (LTCF) species. Hereafter, the LT swards are called mixed swards as a single combination of ryegrass and clovers, whereas LTC and LTCF swards are called MSS as a combination of at least four species from three botanical families. The experimental area (8.7 ha) was divided into four block replicates with a mineral nitrogen fertilisation of 75 kg N/ha per year for each treatment. In total, 13 grazing rotations were carried out by applying the same grazing calendar and the same pasture allowance of 19 kg DM/cow per day above 4 cm for all treatments. Clover represented 20% of DM for mixed and MSS swards; chicory represented 30% of DM for MSS and tall fescue represented 10% of DM for LTCF swards. Higher milk production (+1.1 kg/day) and milk solids production (+0.08 kg/day) were observed for mixed swards than for ryegrass swards. Pasture nutritive value and pasture DM intake were unaffected by the inclusion of clover. Pasture DM, organic matter and NDF concentrations were lower for MSS than for mixed swards. Higher milk production (+0.8 kg/day), milk solids production (+0.04 kg/day) and pasture DM intake (+1.5 kg DM/day) were observed for MSS than for mixed swards. These positive effects of MSS were observed for all seasons, but particularly during summer where chicory proportion was the highest. In conclusion, advantages of grazing MSS on cow performance were due to the cumulative effect of improved pasture nutritive value and increased pasture DM intake that raised milk production and milk solids production.

Foraging behavior and ruminal fermentation of dairy cows grazing ryegrass pasture alone or with white clover

The objective of this work was to evaluate the influence of pasture composition and regrowth age on the relationship between feeding behavior and ruminal fermentation in dairy cows grazing perennial ryegrass with or without white clover. The experiment was carried out in a 2x2 factorial arrangement, with two sward types and two ages of regrowth. Swards of perennial ryegrass sown alone (PRG) and of perennial ryegrass mixed with white clover (GC) were evaluated. Twelve late‑lactation Holstein cows, fistulated at the rumen, were distributed in a 4x4 latin square experimental design with four 12‑day periods. Daily distribution of grazing was similar in the PRG and the GC swards, but the concentration of rumen volatile fatty acids (VFA) was higher and the proportion of propionate was lower on mixed swards during the day. Daily distribution of grazing was similar in pastures of different ages. However, in the oldest swards, rumen fluid pH increased and VFA concentration decreased after evening milking. Time spent grazing does not influence ruminal fermentation, which depends on the changes that occur as different sward layers are grazed.

Pasture intake and milk production of dairy cows grazing annual ryegrass with or without corn silage supplementation

The use of corn silage to supplement grazing dairy cows can improve milk production and nutrient intake when the substitution rate is low. This enhancement occurs by increasing the total DM intake. The hypothesis tested in this study was that increasing corn silage supplementation level of dairy cows grazing annual ryegrass at medium pasture allowance could increase substitution rate and decrease milk production response. Three supplementation levels (0, 4 and 8 kg DM/day) were compared for dairy cows strip-grazing annual ryegrass (Lolium multiflorum cv. Common). The study was arranged as a 3 × 3 Latin square design, repeated three times using nine Holstein lactating cows. The supplement was a 7 : 1 mixture based on the DM of corn silage and soybean meal and was offered individually twice daily after the morning and afternoon milkings. Each treatment group of cows grazed separately at a common daily pasture allowance of 35 kg DM/cow to ground level. Each experimental period was 12 days, with an 8-day adaptation and a 4-day measurement period. The individual pasture intake was measured from Day 9 to Day 12 using the n-alkane technique. The daily pattern of grazing and ruminating times were measured by visual observations. The supplement DM intake was lower than expected, averaging 3.0 and 4.3 kg DM/day for cows receiving 4 and 8 kg DM/day, respectively. Pasture and supplement energy value were 7.0 and 6.3 MJ of NEL/kg DM, respectively. The substitution rate averaged 0.2 and was unaffected by the supplementation level. The pasture intake was similar for all treatments (14.0 kg of DM/day), and total DM intake and milk production (+0.5 kg of milk/kg DM of supplement) increased linearly with increasing supplementation level. The daily grazing time was shorter by 111 min/day for the supplemented cows than for the unsupplemented cows. Cows grazing the annual ryegrass at medium pasture allowance improved their total DM intake and individual performance when supplemented with corn silage.