Grass Dry Matter Intake Research Articles

The effect of initial spring grazing date and subsequent stocking rate on the grazing management, grass dry matter intake and milk production of dairy cows in summer

AbstractThe objective of this study was to investigate the effects of an early (February; F) or delayed (April; A) primary spring grazing date and two stocking rates, high (H) and medium (M), on the grazing management, dry matter (DM) intake of grass herbage and milk production of spring‐calving dairy cows grazing a perennial ryegrass sward in the subsequent summer. Sixty‐four Holstein‐Friesian dairy cows (mean of 58 d in milk) were assigned to one of four grazing treatments (n = 16) which were imposed from 12 April to 3 July 2004. Cows on the early spring‐grazing treatment were grazed at 5·5 cows ha−1 (treatment FH) and 4·5 cows ha−1 (treatment FM) while cows on the late‐grazing treatment were grazed at 6·4 cows ha−1 (treatment AH) and 5·5 cows ha−1 (treatment AM). The organic matter digestibility and crude protein concentration of the grass herbage were higher on the early‐grazing treatment than on the late‐grazing treatment. The cows on the FM treatment had significantly (P < 0·001) higher milk (24·5 kg), solids‐corrected milk (22·5 kg), fat (P < 0·01, 918 g) and protein (831 g) yields than the other three treatments. Cows on the FM treatment had a higher (P < 0·001) DM intake of grass herbage by 2·3 kg DM per cow per day than cows on the AH treatment, which had a DM intake significantly lower than all other treatments (15·2 kg DM per cow per day). The results of the present study showed that grazing in early spring has a positive effect on herbage quality in subsequent grazing rotations. The study also concluded that early spring‐grazed swards stocked at a medium stocking rate (4·5 cows ha−1; FM) resulted in the highest DM intake of grass herbage and milk production.

The effect of strain of Holstein-Friesian dairy cow and pasture-based system on grass intake and milk production

AbstractThe objective of this study was to investigate the effects of strain of Holstein-Friesian cow, pasture-based feeding system (FS) and their interaction on milk production, dry matter (DM) intake and energy balance over 3 years consecutively. The three strains were: high milk production North American (HP), high fertility and survival (durability) North American (HD) and New Zealand (NZ). The FS were: a high grass allowance (HG FS), a high concentrate (HC FS) and a high stocking rate (HS FS). A separate farmlet existed for each FS and a total of 99, 117 and 117 animals were used in year 1, year 2 and year 3, respectively, divided equally between strains and FS. Individual animal intakes were estimated three times each year at pasture; in May (P1), in July (P2) and October (P3), corresponding on average to day 102, 177 and 240 of lactation, respectively. The HP cows achieved the highest milk yield, the NZ the lowest, while the HD was intermediate; the HP achieved the highest solid corrected milk yield with no difference between the NZ and HD strains. The grass DM intake of the HP strain was highest ( P<0·001) in all feeding systems. There was a significant strain×FS interaction for yield of milk, fat and protein, grass DM and total DM intake. The milk production response to the HC FS in P1 and P2 was significantly greater for both the HP and HD strains than for the NZ strain, while in P3 the response was highest for the HP, lowest for the NZ and intermediate for the HD. The reduction in pasture DM intake per kg of concentrate was greatest for the NZ strain, lowest for the HP and intermediate for the HD strain. The NZ strain also had the highest grass DM intake per kg live weight. The existence of strain×FS interactions for production and DM intake indicate that greater knowledge of both genotype and feeding environment is required to predict animal performance.

The Effect of Concentrate Supplementation on Nutrient Flow to the Omasum in Dairy Cows Receiving Freshly Cut Grass

An experiment was carried out to determine the effect of increasing the amount of grain-based concentrate (0, 3, or 6kg/d) on nutrient flow to the omasum, rumen fermentation pattern, milk yield, and nutrient use of dairy cows. Harvested timothy-meadow fescue grass was fed individually 3 times daily to 6 rumen-cannulated Holstein-Friesian cows in a duplicated 3×3 Latin square experiment. Grass was offered as 6 equal meals daily, and concentrates were fed as 2 equal meals daily. Nitrogen, microbial N, and neutral detergent fiber (NDF) flow from the rumen were measured using an omasal sampling technique in combination with a triple marker method [CoEDTA, Yb, and indigestible NDF (INDF) as markers]. Concentrate supplementation linearly decreased ruminal pH, N degradability, ammonia N concentration, and molar proportion of acetate and increased the molar proportion of butyrate. Supplementation of grass with concentrates linearly increased dry matter intake (DMI), microbial N synthesis, N, and NDF flow to the omasum, and ruminal and total tract NDF digestibility decreased linearly. Decreases in NDF digestibility in response to concentrates was primarily related to a decrease in the rate of digestion. Increased DMI overcame the negative effects of concentrate on NDF digestion, resulting in a linear increase in total metabolizable energy intake and milk production. Physical constraints were found not to limit grass DMI. Concentrate supplementation increased the apparent use of dietary N for milk production because of a reduction in N intake, rather than thorough improvements in N capture in the rumen.

The relationship between milk production potential and herbage intake of grazing dairy cows

AbstractThe objective of this trial was to examine the daily herbage requirement and grass dry matter intake (DMI) of dairy cows of different levels of milk production with rotational grazing and optimum grazing conditions. The daily herbage allowance (DHA) that was required was defined as the allowance that permitted the herds to graze to a post-grazing sward height (SHA) of 70 mm. Four herds of 15 primiparous Holstein-Friesian cows were assembled with similar characteristics but different milk production potentials. The herds grazed separately and were offered a DHA such that the SHA was 70 mm for all herds. The daily yield per cow, for the 4 weeks prior to the start of the experiment (PMY), was 17·4, 19·8, 21·8 and 24·3 kg milk (s.e.0·20, P < 0·001), 0·72, 0·78, 0·87 and 0·93 kg fat (s.e. 0·021, P < 0·001), 0·59, 0·66, 0·71 and 0·77 kg protein (s.e. 0·009, P < 0·001) for herds 1 to 4, respectively. The experiment began on 30 June and finished on 16 August. The swards offered were 18-day re-growths following a previous defoliation by grazing. Herbage mass pre- and post-grazing was 2143 (s.e.33·3) and 622 (s.e.18·2) kg dry matter (DM) per ha above 40 mm, respectively and were similar for the four herds. The DHA was 21·2, 21·9, 22·9 and 23·9 (s.e. 0·13, P < 0·001) kg DM per cow above 40 mm. Individual cow grass DMI was determined once during the experimental period using the alkane technique. Experimental milk yield (EMY) was 15·1, 17·4, 18·6 and 20·8 (s.e. 0·33, P < 0·001) kg per cow per day. DMI was 14·5, 15·4, 15·5 and 16·1 (s.e. 0·47, P > 0·05). Variations in DMI were best described by the relationship: DMI = 0·85 (s.e. 3·038) + 0·32 (s.e. 0·082) ✕ EMY + 0·012 (s.e. 0·0054) ✕ experimental live weight + 2·10 (s.e. 0·738) ✕ weight gain + 0·020 (s.e. 0·0085) ✕ days in milk (residual s.d. = 1·477 and r = 0·75). EMY was linked to DMI and PMY according to the expression: EMY = –0·64 (s.e. 1·532) + 0·256 (s.e. 0·0865) ✕ DMI + 0·705 (s.e. 0·0620) ✕ PMY (residual s.d. = 1·204 and r = 0·872). It is concluded that higher yielding herds require higher DHA and this is associated with higher DMI of those herds.

The effect of grass cultivars differing in heading date and ploidy on the performance and dry matter intake of spring calving dairy cows at pasture

The system of milk production in Ireland is dependent on the efficient utilisation of grazed grass. Therefore the use of grass cultivars with different heading dates may have a large effect on dairy cow performance. The objective of this study was to determine the effect of grass cultivars differing in heading date and grass ploidy on milk production and grass dry matter intake (GDMI) of spring calving dairy cows. The study took place over two years. Seventy-two spring calving dairy cows in Year 1 and 80 in Year 2 were blocked into groups of four and were assigned randomly to one of four grass cultivar treatments. The grass cultivars differed in heading date (intermediate or late) and grass ploidy (diploid or tetraploid). The grazing season began in April 12 (Year 1) and April 25 (Year 2) and lasted until the end of September in both years. A total concentrate DM input of 248 kg and 45 kg·cow -1 was offered to the herds in Year 1 and in Year 2, respectively. All concentrate was of- fered during the first 3 grazing rotations. Rotation had a significant effect (P < 0.001) on all milk pro- duction parameters in both years. In Year 1, late heading cultivars significantly (P < 0.05) increased milk yield, solids corrected milk yield (SCM), fat, protein and lactose yield. There was a significant interaction (P < 0.05) between heading date and grass ploidy for lactose yield and fat concentration. In Year 2, late heading cultivars had also increased milk yield (P < 0.01), lactose yield (P < 0.05), SCM (P < 0.05), protein yield (P < 0.001) and protein concentration (P < 0.05). In Year 1, the GDMI was higher (P < 0.001) for cows grazing the late heading cultivars. It is concluded that later heading grass cultivars have a beneficial effect on the milk production performance of spring calving dairy cows.

Effect of Genetic Merit and Concentrate Supplementation on Grass Intake and Milk Production with Holstein Friesian Dairy Cows

A total of 48 high genetic merit (HM) and 48 medium merit (MM) cows, each given a low (LC), medium (MC), or high (HC) level of concentrate supplementation, were used in a split-plot design experiment, which was run in three consecutive years, to evaluate animal production responses. Individual cow intakes were estimated twice each year while at pasture; measurement period 1 (MPI) was in May/June, and measurement period 2 (MP2) was in early September, corresponding on average to d 110 and 200 of lactation, respectively. In MP1, cows were offered 0 (LC), 3 (MC), and 6kg (HC), whereas in MP2 the levels were 0 (LC), 0 (MC), and 4kg (HC) of concentrate daily. Genotype had a significant effect on all milk production parameters in MP1 and MP2. The HM cows had the highest yield of milk, fat, protein, and lactose, whereas the MM cows had the highest milk fat, protein, and lactose concentrations. The HM cows had significantly higher grass dry matter intake (GDMI) estimates. In MP1, the average responses, per kg concentrate dry matter, was +1.10kg of milk, +0.038kg of protein, +0.032kg of fat. The corresponding values in MP2 were +0.94kg of milk, +0.037kg of protein, and +0.025kg of fat. The response to concentrate was linear and independent of preexperimental milk yield. In MP1, the partial regression coefficients relating daily GDMI to an increase in 1kg of preexperimental milk yield (PMY), preexperimental BW (PBW), and concentrate intake (CI) were 0.123, 0.006, and −0.54, respectively, whereas the corresponding values in MP2 were 0.190, 0.007, and −0.444, respectively. This study indicates that with high yielding dairy cows, on gras only GDMI of 17kg of supporting milk yield of 30-kg/d is achievable. In this scenario, concentrate supplementation will result in lower substitution rates, and higher milk yield response than previously published with lower yielding cows.

Increased concentration of water‐soluble carbohydrate in perennial ryegrass (Lolium perenne L.): milk production from late‐lactation dairy cows

Eight multiparous Holstein–Friesian dairy cows in late lactation were used to investigate the potential of using perennial ryegrass with a high concentration of water‐soluble carbohydrate (WSC) to increase the efficiency of milk production. After a pretreatment period on a common pasture, the cows were each given ad libitum access to one of two varieties of zero‐grazed grass continuously for 3 weeks. Treatments were: high sugar (HS), an experimental perennial ryegrass variety bred to contain high concentrations of WSC; or control, a standard variety of perennial ryegrass (cv. AberElan) containing typical concentrations of WSC. The two grass varieties were matched in terms of heading date. All animals also received 4 kg day–1 standard dairy concentrate. Grass dry matter (DM) intake was not significantly different between treatments (11·6 vs. 10·7 kg DM day–1; s.e.d. 0·95 for HS and control diets respectively), although DM digestibility was higher on the HS diet (0·71 vs. 0·64 g g–1 DM; s.e.d. 0·23; P &lt; 0·01) leading to higher digestible DM intakes for that diet. Milk yield from animals offered the HS diet was higher (15·3 vs. 12·6 kg day–1; s.e.d. 0·87; P &lt; 0·05) and, although milk constituent concentrations were unaffected by treatment, milk protein yields were significantly increased on the HS diet. The partitioning of feed N was significantly affected by diet, with more N from the HS diet being used for milk production (0·30 vs. 0·23 g milk N g–1 feed N; s.e.d. 0·012; P &lt; 0·01) and less being excreted in urine (0·25 vs. 0·35; s.e.d. 0·020; P &lt; 0·01). In a separate experiment, using the same grasses harvested earlier in the season, the fractional rate of DM degradation, measured by in situ and gas production techniques, was higher for the HS grass than for the control. It is concluded that increased digestible DM intakes of the HS grass led to increased milk yields, whereas increased efficiency of utilization of the HS grass in the rumen resulted in the more efficient use of feed N for milk production and reduced N excretion.

Estimativa do Consumo Voluntário do Capim-Tanzânia (Panicum maximum, Jacq. cv. Tanzânia) por Vacas em Lactação sob Pastejo Rotacionado

O estudo foi conduzido numa área de capim-Tanzânia (Panicum maximum), manejada em pastejo rotacionado para estimar o consumo de matéria seca de vacas em lactação. Os três tratamentos foram: vacas mestiças alimentadas com 3 kg de concentrado e vacas mestiças e Zebu (Gir) sem suplementação com concentrado. Observou-se uma quantidade de 7340,2 kg de matéria seca (MS) /ha de forragem disponível antes da ocupação e de 5.639,5 após o 3° dia de ocupação. O consumo de MS de capim-Tanzânia foi 8,26 ± 5,66, 11,01 ± 5,37 e 9,55 ± 2,31 kg de MS/vaca/dia ou 2,15%, 2,37% e 2,34% do peso vivo, respectivamente para as vacas suplementadas, cruzadas não suplementadas e vacas Zebu . A média da produção de leite foi maior para o grupo suplementado (11,98 kg/vaca/dia). A produção de leite observada para as vacas não suplementadas foi similar. Produção de leite de 6,53 foi obtida pelas vacas cruzadas não suplementadas e 5,46 por vaca/dia foi produzida pelas vacas Zebu.

The relationship between genetic merit for yield and live weight, condition score, and energy balance of spring calving Holstein-Friesian dairy cows on grass based systems of milk production

AbstractThe objective of this study was to estimate the effects of genetic merit for milk yield on energy balance (EB), dry matter intake (DMI), and fertility for cows managed on three different grass based feeding systems, and to estimate possible interactions between genetic merit and feeding system. Individual animal intake estimates were obtained at pasture on 11 occasions across three grazing seasons. The data set contained 96 first lactation animals in 1995, 96 second lactation animals in 1996, and 72 third lactation animals in 1997. Half of these animals were of high (HG), and half of medium genetic merit (MG) for milk solids production. Genetic effects for the traits of interest were estimated as the contrast between the two genetic groups, and by the genetic regression of phenotypic performance on the estimated breeding value for fat and protein yield, based on pedigree information alone (PI). Significant effects of feeding system were observed on yields, DMI and EB, whereas there was no effect on live weight, condition score or reproductive performance. The interaction between genetic merit and feeding system was not significantly different from zero for any of the traits. Yields, grass DMI, and total DMI were all higher for HG than for MG, and also positively correlated (P&lt;0.001) with PI. Furthermore, condition score, conception to first and second service, and pregnancy rate were significantly negatively correlated with PI. While at pasture, EB was positively (P&lt;0.01) correlated with PI, although the contrast between HG and MG was not significantly different from zero. Condition score changes during very early lactation, demonstrated that HG had a more negative EB than MG. The results clearly illustrate the production potential of HG cows on grass based systems, however the reduced reproductive performance questions their suitability for seasonal calving systems.

Pasture availability and dry matter intake of lactating crossbred cows grazing elephant grass ( Pennisetum purpureum, Schum.)

The trial was carried out in Brazil, from April 1992 to October 1993. Availability and voluntary dry matter intake (DMI) of elephant grass ( Pennisetum purpureum) were evaluated, using three groups of 24 crossbred lactating cows, grazing (4.5 cows/ha), during three days, paddocks varying in size (607, 494 and 417 m 2) according to the resting periods adopted. The following treatments were studied: resting period of 30 days without (30W) and resting periods of 30 (30C), 37.5 (37.5C) and 45 (45C) days with 2 kg/day (20.6% crude protein CP) concentrate supplement. From October to June the elephant grass was the sole forage, while during the dry season, cows received sugarcane plus 1% urea as roughage supplement. The average chemical composition of sugarcane mixture was: 10.1% CP, 52.5% neutral detergent fiber (NDF), 31.6% acid detergent fiber (ADF), 58.5% in vitro dry matter digestibility (IVDMD) and the average daily intake was 1.3 ± 0.2% of body weight (BW). Mean elephant grass availabilities of paddocks 45C (2423±92 kg of DM/ha) was greater ( p < 0.05) than (1745 and 1939 ± 92 kg of DM/ha) observed, respectively, for resting periods of 30 and 37.5 days. Daily herbage allowance was similar among treatments (11.3 ± 0.45 kg of DM/cow), but varied according to the season and year, being higher in summer, intermediate in autumn and spring and lower in winter. As the dry season was more severe in winter and spring 1993, daily herbage allowance was smaller than that in 1992. Extrusa composition was affected by the resting period ( p < 0.05), CP content decreased (0.1%) and NDF increased (0.09%) for each day beyond the 30th day of the resting periods. Total DMI estimated using chromic oxide, was lower ( p < 0.05) for non-supplemented (2.7 ± 0.12% BW) than supplemented animals (3.0 ± 0.12% BW). The elephant grass DMI varied from 1.2% (winter) and 3.7 ± 0.10% BW (summer) being similar among experimental treatments, except during the summer. In that season elephant grass DMI was smaller only in 45C in relation to 37.5C, while those observed in 30W and 30C were similar and did not differ from 37.5C. The average daily milk production (11.4 kg/cow) did not vary among treatments. Although the 30 day resting period resulted in a better quality herbage intake, it did not reflect a higher DMI or milk production. The season and, consequently, the amount of rainfall influenced the results during the year.

The effect of cow genetic index and grass-based feeding system on the performance of spring-calving Holstein-Friesian cows in second lactation

AbstractThe objective of this study was to investigate the effect of both cow genetic index (CGI) and feeding system on the performance of second lactation Holstein-Friesian dairy cows on grass-based feeding systems. There was no interaction between CGI and feeding system for any of the parameters measured. Cows of high genetic index (HGI) produced significantly higher yields of milk (P &lt; 0.001), fat (P &lt; 0.001) protein (P &lt; 0.0001) and lactose (P &lt; 0.001) than medium genetic index cows (MGI). CGI had no effect on the concentration of milk constituents. Averaged across four intake measurements the HGI cows had significantly (P &lt; 0.001) higher grass dry-matter intake (GDMI) and total dry-matter intake (TDMI). Live weight was similar for both genotypes during lactation. The HGI cows had significantly (P &lt; 0.05) higher live-weight loss in the first 10 weeks of lactation, significantly lower live-weight gain from week 10 to the end of lactation and higher (P &lt; 0.05) live-weight gain during the dry period. Condition score was significantly lower with the HGI (P &lt; 0.001) at all stages of lactation. There was a higher proportion (P &lt; 0.05) of the HGI cows non-pregnant at the end of the 13-week breeding season. Feeding system had a significant effect on the yield of milk (P &lt; 0.001), fat (P &lt; 0.001), protein (P &lt; 0.001) and lactose (P &lt; 0.001). Feeding system B produced significantly higher (P &lt; 0.05) milk yield and yield of constituents (when compared with feeding systems A and C). Over the period when feeding systems were being applied, feeding system C had significantly higher (P &lt; 0.05) milk protein concentration. Feeding system had a significant effect (P &lt; 0.001) on both GDMI and TDMI. Feeding system had no effect on live weight, condition score or fertility performance.

Effect of dried Gliricidia sepium leaf supplement on feed intake, digestibility and nitrogen retention in sheep fed dried KW4 elephant grass (Pennisetum purpureum) ad libitum

A feeding experiment was conducted to study the effects of supplementation with dried Gliricidia sepium leaves on dry matter (DM) intake, digestibility and nitrogen retention in sheep fed KW4 elephant grass. Four mature rams were fed elephant grass ad libitum supplemented with four levels of gliricidia leaves (0, 4, 8 and 12 g DM kg−1 lwt day−1) in a 4 × 4 Latin square design. Supplementation with gliricidia leaves decreased elephant grass DM intake (g DM day−1 or g DM kg−1 BW0.75 day−1). However, the effect of supplementation on total DM intake of the rations was not significant (P >; 0.05). Total crude protein intake significantly (P < 0.001) increased with increasing levels of gliricidia supplementation. Total DM digestibility and body weight changes were significantly (P < 0.05) improved by gliricidia supplementation; with the highest digestibility coefficient (60.5%) and body weight gain (89.3 g/day) obtained at 8 g DM kg−1 lwt day−1. Gliricidia supplementation significantly (P < 0.001) improved nitrogen intake, absorbed nitrogen and retained nitrogen but with no significant difference at 8 and 12 g DM kg−1 lwt day−1 level of supplementation. The highest efficiency of N retention by sheep (44.9%) was obtained at 8 g DM kg−1 lwt day−1 level of gliricidia supplementation. The results indicated that supplemention of KW4 elephant grass with small quantities of gliricidia leaves up to 8 g DM kg−1 lwt day−1 enhance utilisation efficiency of the total ration. Further increases in the level of gliricidia supplementation, under the conditions of this experiment, reduced the intake of elephant grass leading to substitution effects of the basal.

Rumen Fermentation and Nutrient Flows for Cows Fed Grass and Grass Supplemented with Molassed Beet Pulp Pellets

An experiment was carried out to determine the effect of a grass diet and a concentrate supplement on rumen fermentation and nutrient flows to the duodenum. Perennial ryegrass was cut and fed indoors to eight rumen- and duodenum-cannulated Friesian cows with or without 3 kg/d of molassed beet pulp in a randomized design experiment. The dry matter intake of grass was significantly lower for cows fed the concentrate supplement (13.6 vs. 11.5kg of dry matter/d), but total dry matter and organic matter (OM) intakes were similar for cows fed both diets. Cows fed the supplement had higher mean concentrations of total volatile fatty acids (108 vs. 89 mmol/L) and a higher percentage of butyrate in total volatile fatty acids (13.5 vs. 11.6 mol/100mol). There were no differences between the diets in the flow of OM to the duodenum or in the extent of OM digestion in the rumen. Flows of nonammonia N, microbial N, and amino acids to the duodenum tended to be higher for cows fed the supplemented diet than for those fed ryegrass only. The efficiency of microbial protein synthesis also tended to be higher for cows fed the supplemented diet (42 vs. 37.7 g/kg of OM apparently digested in the rumen and 28.2 vs. 26 g/kg of OM truly digested in the rumen). Overall, there were indications that the supplement caused better capture of N in the rumen and increased the efficiency of microbial protein synthesis.

Rice bran as a supplement to elephant grass for cattle and buffalo in Indonesia: 1. Feed intake, utilization and growth rates

SUMMARYIndonesian Ongole and swamp buffalo bulls were fed ad libitum a diet of elephant grass (Pennisetum purpureum) with five levels of rice bran (0, 1·2, 2·4, 3·6 and 4·8 kg/head/ day) in a study lasting 161 days. Measurements were made of the digestibility of the diet, the balances of nitrogen, phosphorus, calcium and water and the metabolizability of the gross energy. Using multiple regressions, the daily intakes of metabolizable energy were partitioned between maintenance and growth.Feeding rice bran stimulated appetite, initially improved feed conversion efficiency and increased growth rates. Each additional kilogram of rice bran fed depressed grass dry-matter intake by 0·8 kg in the buffaloes and 0·6 kg in Ongoles. Rice bran had little effect on digestibility of dry matter, organic matter and energy. Metabolizable energy contents of rice bran and elephant grass were calculated to be, respectively, 9·5 and 8·2 MJ/kg dry matter. Nitrogen and phosphorus status was improved in the supplemented animals but the balance of calcium was adversely affected. Voluntary feed intake was always higher in the buffaloes but the differences were reduced with increasing rice-bran supplementation.Metabolizable energy requirements for maintenance and growth did not differ significantly between Ongole and buffaloes and were similar to values calculated for British animals.

Título en español

Los registros de producción de leche, porcentaje de grasa láctea, peso del animal, reproducción y salud de 362 vacas en 506 partos se utilizaron para estimar la eficiencia de utilización de los pastos tropicales por vacas lactantes pastando exclusivamente o pastando con suplementación. Se evaluaron 7 sistemas de alimentación: pasto exclusivamente (T1); pasto más suplementación con maíz molido (T2); con melaza (T3); con alimento concentrado (T5) o con urea-melaza (T6); a razón de 1.0 kg por cada 2.0 kg de leche en exceso de 10 kg de leche por día; o pasto más alimento concentrado a razón de 1.0 kg par cada 2.0 kg de leche, independientemente de la producción de leche, al usar una densidad de pastoreo de 2.5 (T4) 65.0 (T7) vacas por ha. Todos los sistemas de suplementación arrojaron producciones significativamente mayores de leche, grasa, y leche corregida para contenido de grasa, que las en el sistema de pasto exclusivamente (T1). El contenido de grasa parece depender del consumo de los pastos. La suplementación también extendió el período de producción lechera. Se obtuvieron diferencias significativas entre los efectos de los sistemas de alimentación en cuanto a la ganancia de peso, el tiempo que tomó alcanzar la máxima producción de leche, el nivel de la producción máxima, la persistencia en la producción de leche, el intervalo entre el parto y la concepción subsiguiente, el tiempo desde el primer cruzamiento hasta la concepción y el intervalo entre partos. Los elevados niveles de suplementación (T4, T7), aumentaron la ganancia de peso, la persistencia productiva y el tiempo necesario para alcanzar la producción máxima, pero disminuyó la eficiencia reproductiva. En los niveles medianos de suplementación (T3, T5, T6), la eficiencia (Meal/kg materia seca) de la utilización del suplemento para la producción de leche fue satisfactoria. Sin embargo, no ocurrió lo mismo en los niveles elevados de suplementación (T4, T7). Los suplementos (concentrados) tan o más ricos en nitrógeno no proteínico o proteína bruta que el maíz o la melaza, proveyeron una mejor eficiencia de utilización. Durante los primeros 150 días de lactancia (T1), las vacas consumieron una media de 14.3 kg de materia seca del pasto por día, 62.9% del peso corporal. Las vacas en suplementación baja (T2, T3, T5, T6) arrojaron de 24 a 29% menos, y las que recibieron suplementación alta casi el 60% menos de consumo. El tipo de suplementación influyó limitadamente el consumo de la materia seca del pasto. Cuando el potencial genético para producir leche sobrepasó los 3000 kg, la alimentación suplementaria pareció económicamente factible. Aun con fertilización intensiva, se obtuvo una respuesta lineal con el nivel de suplementación proteínica. La alimentación suplementaria causó una alta tasa de sustitución en los pastos tropicales. Por esta razón, se reduce la eficiencia en el uso de la materia seca del pasto a menos que la densidad de pastoreo sea cuidadosamente ajustada.

The voluntary intake of roughages by pregnant and by lactating dairy cows

SUMMARY1. Effects of late pregnancy and early lactation on the voluntary intake of dried grass (Expt 1) and a poor quality seeds hay (Expt 2) by dairy cows are described. Each cow received a constant daily allocation of concentrates throughout late pregnancy. After calving half the cows received an 80% increase in concentrates, and the remainder continued to receive their pre-partum allowance.2. Mean daily intakes of dried grass were higher than those of poor quality seeds hay. Intake of dried grass in week 2 of lactation was significantly correlated with the live weight of the cows, but a non-significant correlation was observed when seeds hay was offered.3. During late pregnancy mean daily intakes of both roughages were approximately constant until the week immediately before par turition, when a significant decline occurred.4. After calving mean daily intakes of both roughages increased throughout the first six weeks of lactation by 20–30% of the intake at week 1 post partum.5. The 80% increase in daily concentrate allocation in early lactation caused a significant decline of 0·55 kg dried grass dry-matter intake per kg concentrate dry matter; the decline of 0·17 kg poor quality hay dry matter per kg concentrate dry matter was not significant.