Effect of forage conservation method on plasma lipids, mammary lipogenesis, and milk fatty acid composition in lactating cows fed diets containing a 60:40 forage-to-concentrate ratio

The effects of forage conservation method on plasma lipids, mammary lipogenesis, and milk fat were examined in 2 complementary experiments. Treatments comprised fresh grass, hay, or untreated (UTS) or formic acid treated silage (FAS) prepared from the same grass sward. Preparation of conserved forages coincided with the collection of samples from cows fed fresh grass. In the first experiment, 5 multiparous Finnish Ayrshire cows (229 d in milk) were used to compare a diet based on fresh grass followed by hay during 2 consecutive 14-d periods, separated by a 5-d transition during which extensively wilted grass was fed. In the second experiment, 5 multiparous Finnish Ayrshire cows (53 d in milk) were assigned to 1 of 2 blocks and allocated treatments according to a replicated 3 × 3 Latin square design, with 14-d periods to compare hay, UTS, and FAS. Cows received 7 or 9 kg/d of the same concentrate in experiments 1 and 2, respectively. Arterial concentrations of triacylglycerol (TAG) and phospholipid were higher in cows fed fresh grass, UTS, and FAS compared with hay. Nonesterified fatty acid (NEFA) concentrations and the relative abundance of 18:2n-6 and 18:3n-3 in TAG of arterial blood were also higher in cows fed fresh grass than conserved forages. On all diets, TAG was the principle source of fatty acids (FA) for milk fat synthesis, whereas mammary extraction of NEFA was negligible, except during zero-grazing, which was associated with a lower, albeit positive calculated energy balance. Mammary FA uptake was higher and the synthesis of 16:0 lower in cows fed fresh grass than hay. Conservation of grass by drying or ensiling had no influence on mammary extraction of TAG and NEFA, despite an increase in milk fat secretion for silages compared with hay and for FAS than UTS. Relative to hay, milk fat from fresh grass contained lower 12:0, 14:0, and 16:0 and higher S3,R7,R11,15-tetramethyl-16:0, cis-9 18:1, trans-11 18:1, cis-9,trans-11 18:2, 18:2n-6, and 18:3n-3 concentrations. Even though conserved forages altered mammary lipogenesis, differences in milk FA composition were relatively minor, other than a higher enrichment of S3,R7,R11,15-tetramethyl-16:0 in milk from silages compared with hay. In conclusion, differences in milk fat composition on fresh grass relative to conserved forages were associated with a lower energy balance, increased uptake of preformed FA, and decreased synthesis of 16:0 de novo in the mammary glands, in the absence of alterations in stearoyl-coenzyme A desaturase activity.

The effect of adding stinging nettle (Urtica dioica) haylage to a total mixed ration on performance and rumen function of lactating dairy cows

In vitro studies found that inclusion of dried stinging nettle (Urtica dioica) at 100 mg/g dry matter (DM) increased the pH of a rumen fluid inoculated fermentation buffer by 30% and the effect was persistent for 7 days. Our objective was to evaluate the effects of adding stinging nettle haylage to a total mixed ration on feed intake, eating and rumination activity, rumen pH, milk yield, and milk composition of lactating dairy cows. Six lactating Holstein-Friesian cows were used in a replicated 3 × 3 Latin Square design experiment with 3 treatments and 3 week periods. Treatments were a control (C) high-starch (311 g/kg DM) total mixed ration diet and two treatment diets containing 50 (N5) and 100 (N10) g nettle haylage (DM/kg) as a replacement for ryegrass silage (Lolium perenne). There was an increase (linear, P < 0.010) in the proportion of large particles and a reduction in medium (linear, P = 0.045) and fine particles (linear, P = 0.026) in the diet offered with increasing nettle inclusion. A numerical decrease (linear, P = 0.106) in DM intake (DMI) was observed as nettle inclusion in the diet increased. Milk yield averaged 20.3 kg/day and was not affected by diet. There was a decrease (quadratic, P = 0.01) in the time animals spent ruminating as nettle inclusion in the diet increased, in spite of an increase in the number of boli produced daily for the N5 diet (quadratic, P = 0.031). Animals fed the N10 diet spent less time with a rumen pH below 5.5 (P < 0.05) than cows fed the N5 diet. Averaged over an 8.5 h sampling period, there were no changes in the concentration or proportions of acetate or propionate in the rumen, but feeding nettle haylage reduced the concentrations of n-butyrate (quadratic, P < 0.001), i-butyrate (linear, P < 0.009) and n-caproate (linear, P < 0.003). Milk and fat and protein corrected milk yield were not affected when nettles replaced ryegrass silage in the diet of lactating dairy cows, despite a numerical reduction in feed intake. Rumination activity was reduced by the addition of nettle haylage to the diet, which may reflect differences in fibre structure between the nettle haylage and ryegrass silage fed. Changes observed in rumen pH suggest potential benefits of feeding nettle haylage for reducing rumen acidosis. However, the extent to which these effects were due to the fermentability and structure of the nettle haylage compared to the ryegrass silage fed, or a bioactive component of the nettles, is not certain

Effects of 3-nitrooxypropanol on methane emission,digestion, and energy and nitrogen balance of lactating dairy cows

The objective was to measure effects of 3-nitrooxypropanol (3NP) on methane production of lactating dairy cows and any associated changes in digestion and energy and nitrogen metabolism. Six Holstein-Friesian dairy cows in mid-lactation were fed twice daily a total mixed ration with maize silage as the primary forage source. Cows received 1 of 3 treatments using an experimental design based on two 3 × 3 Latin squares with 5-wk periods. Treatments were a control placebo or 500 or 2,500 mg/d of 3NP delivered directly into the rumen, via the rumen fistula, in equal doses before each feeding. Measurements of methane production and energy and nitrogen balance were obtained during wk 5 of each period using respiration calorimeters and digestion trials. Measurements of rumen pH (48 h) and postprandial volatile fatty acid and ammonia concentrations were made at the end of wk 4. Daily methane production was reduced by 3NP, but the effects were not dose dependent (reductions of 6.6 and 9.8% for 500 and 2,500 mg/d, respectively). Dosing 3NP had a transitory inhibitory effect on methane production, which may have been due to the product leaving the rumen in liquid outflow or through absorption or metabolism. Changes in rumen concentrations of volatile fatty acids indicated that the pattern of rumen fermentation was affected by both doses of the product, with a decrease in acetate:propionate ratio observed, but that acetate production was inhibited by the higher dose. Dry matter, organic matter, acid detergent fiber, N, and energy digestibility were reduced at the higher dose of the product. The decrease in digestible energy supply was not completely countered by the decrease in methane excretion such that metabolizable energy supply, metabolizable energy concentration of the diet, and net energy balance (milk plus tissue energy) were reduced by the highest dose of 3NP. Similarly, the decrease in nitrogen digestibility at the higher dose of the product was associated with a decrease in body nitrogen balance that was not observed for the lower dose. Milk yield and milk fat concentration and fatty acid composition were not affected but milk protein concentration was greater for the higher dose of 3NP. Twice-daily rumen dosing of 3NP reduced methane production by lactating dairy cows, but the dose of 2,500 mg/d reduced rumen acetate concentration, diet digestibility, and energy supply. Further research is warranted to determine the optimal dose and delivery method of the product. Key words: 3-nitrooxypropanol, methane, digestion, rumen, dairy cow

Methane emissions from cattle: estimates from short-term measurements using a Green Feed system compared with measurements obtained using respiration chambers or sulphur hexafluoride tracer

The Green Feed (GF) system (C-Lock Inc., Rapid City, USA) is used to estimate total daily methane emissions of individual cattle using short-term measurements obtained over several days. Our objective was to compare measurements of methane emission by growing cattle obtained using the GF system with measurements using respiration chambers (RC)or sulphur hexafluoride tracer (SF6). It was hypothesised that estimates of methane emission for individual animals and treatments would be similar for GF compared to RC or SF6 techniques. In experiment 1, maize or grass silage-based diets were fed to four growing Holstein heifers, whilst for experiment 2, four different heifers were fed four haylage treatments. Both experiments were a 4 × 4 Latin square design with 33 day periods. Green Feed measurements of methane emission were obtained over 7 days (days 22–28) and com-pared to subsequent RC measurements over 4 days (days 29–33). For experiment 3, 12growing heifers rotationally grazed three swards for 26 days, with simultaneous GF and SF6 measurements over two 4 day measurement periods (days 15–19 and days 22–26).Overall methane emissions (g/day and g/kg dry matter intake [DMI]) measured using GF in experiments 1 (198 and 26.6, respectively) and 2 (208 and 27.8, respectively) were similar to averages obtained using RC (218 and 28.3, respectively for experiment 1; and 209 and 27.7, respectively, for experiment 2); but there was poor concordance between the two methods (0.1043 for experiments 1 and 2 combined). Overall, methane emissions measured using SF6 were higher (P<0.001) than GF during grazing (186 vs. 164 g/day), but there was significant (P<0.01) concordance between the two methods (0.6017). There were fewer methane measurements by GF under grazing conditions in experiment 3 (1.60/day) com-pared to indoor measurements in experiments 1 (2.11/day) and 2 (2.34/day). Significant treatment effects on methane emission measured using RC and SF6 were not evident for GF measurements, and the ranking for treatments and individual animals differed using the GF system. We conclude that under our conditions of use the GF system was unable to detectsignificant treatment and individual animal differences in methane emissions that were identified using both RC and SF6techniques, in part due to limited numbers and timing ofmeasurements obtained. Our data suggest that successful use of the GF system is reliant on the number and timing of measurements obtained relative to diurnal patterns of methane emission.

Effects of forage type and extruded linseed supplementation on methane production and milk fatty acid composition of lactating dairy cows

Replacing dietary grass silage (GS) with maize silage (MS) and dietary fat supplements may reduce milk concentration of specific saturated fatty acids (SFA) and can reduce methane production by dairy cows. The present study investigated the effect of feeding an extruded linseed supplement on milk fatty acid (FA) composition and methane production of lactating dairy cows, and whether basal forage type, in diets formulated for similar neutral detergent fiber and starch, altered the response to the extruded linseed supplement. Four mid-lactation Holstein-Friesian cows were fed diets as total mixed rations, containing either high proportions of MS or GS, both with or without extruded linseed supplement, in a 4 × 4 Latin square design experiment with 28-d periods. Diets contained 500 g of forage/kg of dry matter (DM) containing MS and GS in proportions (DM basis) of either 75:25 or 25:75 for high MS or high GS diets, respectively. Extruded linseed supplement (275 g/kg ether extract, DM basis) was included in treatment diets at 50 g/kg of DM. Milk yields, DM intake, milk composition, and methane production were measured at the end of each experimental period when cows were housed in respiration chambers. Whereas DM intake was higher for the MS-based diet, forage type and extruded linseed had no significant effect on milk yield, milk fat, protein, or lactose concentration, methane production, or methane per kilogram of DM intake or milk yield. Total milk fat SFA concentrations were lower with MS compared with GS-based diets (65.4 vs. 68.4 g/100 g of FA, respectively) and with extruded linseed compared with no extruded linseed (65.2 vs. 68.6 g/100 g of FA, respectively), and these effects were additive. Concentrations of total trans FA were higher with MS compared with GS-based diets (7.0 vs. 5.4 g/100 g of FA, respectively) and when extruded linseed was fed (6.8 vs. 5.6 g/100 g of FA, respectively). Total n-3 FA were higher when extruded linseed was fed compared with no extruded linseed (1.2 vs. 0.8 g/100 g of FA, respectively), whereas total n-6 polyunsaturated FA were higher when feeding MS compared with GS (2.5 vs. 2.1 g/100 g of FA, respectively). Feeding extruded linseed and MS both provided potentially beneficial decreases in SFA concentration of milk, and no significant interactions were found between extruded linseed supplementation and forage type. However, both MS and extruded linseed increased trans FA concentration in milk fat. Neither MS nor extruded linseed had significant effects on methane production or yield, but the amounts of supplemental lipid provided by extruded linseed were relatively small.

Effects of forage source and extruded linseed supplementation on methane emissions from growing dairy cattle of differing body weights

Changes in diet carbohydrate amount and type (i.e., starch vs. fiber) and dietary oil supplements can affect ruminant methane emissions. Our objectives were to measure methane emissions, whole-tract digestibility, and energy and nitrogen utilization from growing dairy cattle at 2 body weight (BW) ranges, fed diets containing either high maize silage (MS) or high grass silage (GS), without or with supplemental oil from extruded linseed (ELS). Four Holstein-Friesian heifers aged 13 mo (BW range from start to finish of 382 to 526 kg) were used in experiment 1, whereas 4 lighter heifers aged 12 mo (BW range from start to finish of 292 to 419 kg) were used in experiment 2. Diets were fed as total mixed rations with forage dry matter (DM) containing high MS or high GS and concentrates in proportions (forage:concentrate, DM basis) of either 75:25 (experiment 1) or 60:40 (experiment 2), respectively. Diets were supplemented without or with ELS (Lintec[AU1: Add manufacturer name and location.]; 260 g of oil/ kg of DM) at 6% of ration DM. Each experiment was a 4 × 4 Latin square design with 33-d periods, with measurements during d 29 to 33 while animals were housed in respiration chambers. Heifers fed MS at a heavier BW (experiment 1) emitted 20% less methane per unit of DM intake (yield) compared with GS (21.4 vs. 26.6, respectively). However, when repeated with heifers of a lower BW (experiment 2), methane yield did not differ between the 2 diets (26.6 g/kg of DM intake). Differences in heifer BW had no overall effect on methane emissions, except when expressed as grams per kilogram of digestible organic matter (OMD) intake (32.4 vs. 36.6, heavy vs. light heifers). Heavier heifers fed MS in experiment 1 had a greater DM intake (9.4 kg/d) and lower OMD (755 g/kg), but no difference in N utilization (31% of N intake) compared with heifers fed GS (7.9 kg/d and 799 g/kg, respectively). Tissue energy retention was nearly double for heifers fed MS compared with GS in experiment 1 (15 vs. 8% of energy intake, respectively). Heifers fed MS in experiment 2 had similar DM intake (7.2 kg/d) and retention of energy (5% of intake energy) and N (28% of N intake), compared with GS-fed heifers, but OMD was lower (741 vs. 765 g/kg, respectively). No effect of ELS was noted on any of the variables measured, irrespective of animal BW, and this was likely due to the relatively low amount of supplemental oil provided. Differences in heifer BW did not markedly influence dietary effects on methane emissions. Differences in methane yield were attributable to differences in dietary starch and fiber composition associated with forage type and source.

Sodium hydroxide enhances extractability and analysis of proanthocyanidins in ensiled sainfoin (onobrychis viciifolia)

Little information exists on the effects of ensiling on condensed tannins or proanthocyanidins. The acetone–butanol–HCl assay is suitable for measuring proanthocyanidin contents in a wide range of samples, silages included, but provides limited information on proanthocyanidin composition, which is of interest for deciphering the relationships between tannins and their bioactivities in terms of animal nutrition or health. Degradation with benzyl mercaptan (thiolysis) provides information on proanthocyanidin composition, but proanthocyanidins in several sainfoin silages have proved resistant to thiolysis. We now report that a pretreatment step with sodium hydroxide prior to thiolysis was needed to enable their analysis. This alkaline treatment increased their extractability from ensiled sainfoin and facilitated especially the release of larger proanthocyanidins. Ensiling reduced assayable proanthocyanidins by 29%, but the composition of the remaining proanthocyanidins in silage resembled that of the fresh plants.

Structural features of condensed tannins affect in vitro ruminal methane production and fermentation characteristics

An in vitro study was conducted to investigate the effects of condensed tannins (CT) structural properties, i.e. average polymer size (or mean degree of polymerization); percentage of cis flavan-3-ols and percentage of prodelphinidins in CT extracts on methane production (CH4) and fermentation characteristics. CT were extracted from eight plants in order to obtain different CT types: black currant leaves, goat willow leaves, goat willow twigs, pine bark, red currant leaves, sainfoin plants, weeping willow catkins and white clover flowers. They were analysed for CT content and CT composition by thiolytic degradation, followed by HPLC analysis. Grass silage was used as a control substrate. Condensed tannins were added to the substrate at a concentration of 40 g/kg, with or without polyethylene glycol (+ or −PEG 6000 treatment) to inactivate tannins, and then incubated for 72 h in mixed buffered rumen fluid from three different lactating dairy cows per run. Total cumulative gas production (GP) was measured by an automated gas production system. During the incubation, 12 gas samples (10 μl) were collected from each bottle headspace at 0, 2, 4, 6, 8, 12, 24, 30, 36, 48, 56 and 72 h of incubation and analyzed for CH4. A modified Michaelis–Menten model was fitted to the CH4 concentration patterns and model estimates were used to calculate total cumulative CH4 production (GPCH4). Total cumulative gas production and GPCH4 curves were fitted using biphasic and monophasic modified Michaelis-Menten models, respectively. Addition of PEG increased GP, GPCH4, and CH4 concentration compared to the −PEG treatment. All CT types reduced GPCH4 and CH4 concentration. All CT increased the half time of GP and GPCH4. Moreover, all CT decreased the maximum rate of fermentation for GPCH4 and rate of substrate degradation. The correlation between CT structure and GPCH4 and fermentation characteristics showed that the proportion of prodelphinidins within CT had the largest effect on fermentation characteristics, followed by average 27 polymer size and percentage of cis-flavan-3-ols.

Viabilidade do confinamento de bovinos com feno de resíduos culturais de soja no sistema triângulo

O presente estudo buscou analisar a viabilidade econômica, agronômica e ambiental de um sistema que está em execução em uma propriedade no norte do estado de Goiás. Esse sistema, denominado Sistema Triângulo, vai de encontro com a Integração Lavoura-Pecuária e busca formas alternativas para o uso dos restos culturais (fardos) de soja fornecendo esse material como volumoso para o gado no sistema de confinamento. Para o estudo da viabilidade, foram usadas as informações da própria fazenda num estudo de caso. Para tal, realizou-se uma revisão quanto à adoção de sistema de produção na área agrícola, quanto às interações dos macronutrientes que seriam retirados das áreas por intermédio dos fardos, o papel da matéria orgânica quanto à sustentabilidade do sistema, o cenário atual dos confinamentos no Brasil e os custos que compõem e determinam a lucratividade dessa atividade. Por ser um estudo de caráter incremental, a viabilidade econômica ficou focada à redução dos custos alimentares. Foram utilizadas informações produzidas pela Fazenda Triângulo que é produtora de soja desde 2002. Sendo assim, foi possível acompanhar a evolução dos teores de macronutrientes (nitrogênio, fósforo, potássio, cálcio, magnésio e enxofre) e do carbono em uma área total de 351 ha. Os resultados mostraram uma estabilidade nos níveis dos macroelementos após o início da retirada dos restos culturais mas, apresentou-se inconclusivo no caso do carbono. Foi estimada também a exportação dos macronutrientes por intermédio da retirada dos fardos das áreas de soja. Levantada a composição química dos fardos, foram estabelecidos seis cenários de reposição via adubação específica e esses custos foram acrescidos de custos de processamento dos fardos e o custo dos outros componentes da dieta no confinamento. Calculado o valor presente líquido para cada um dos cenários e comparando com a alternativa tradicional de dieta de confinamento, onde se usa a silagem de milho como 100% do volumoso, mostrou-se uma redução de até 5,02% nos custos alimentares. Com as práticas agronômicas da produção de soja vigentes hoje, recomenda-se a adoção do Sistema Triângulo com a ressalva de uma necessidade de maiores estudos quando seu impacto nos teores de carbono orgânico no solo.

Avaliação microbiológica e bromatológica da silagem ácida obtida de resíduos da indústria de filetagem de tilápia do Nilo (Oreochromis niloticus)

The experiment constituted in evaluating the acid silage prepared from Nile tilapia (Oreochromis niloticus) filletage industry residues. This silage was prepared in a filetage industry through the residues milling and 5% of ascetic acid addition and stock piling in a period up to until 201 days. Storaged silages in a period of 7, 12, 22, 27, 41, 48, 61, 75, 84, 91, 96, 110, 140, 151, 181, 187 and 201dias were evaluated. Bromatologics analyses of rude protein(PB), etereal extract (EE), humidity (UM), ashes (CZ) and microbiological analyses of Salmonella, total coliforms, faecals and Escherichia coli of the storaged silages in a period of 7, 91 and 201 days were realized. The pH was evaluated in all the storaged periods. Differences (P > 0.05) in the substance of PB, EE, UM and CZ were not observed. A linear increase in PH was observed, being stabilizing in plateau of 4.74. In relation to the microbiological analysis the presence of Salmonella, total coliforms, faecals and E. Coli were not found. Was concluded that the acid silage gotten from tilapia filetage residues produced with the use of 5% ascetic acid can be stored during 201 days without having Salmonella, total coliforms and faecals proliferation.

Viabilidade econômica, desempenho e características de carcaça de garrotes em confinamento alimentados com dietas contendo silagem de capins tanzânia ou marandu ou silagem de milho

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dinâmica fermentativa e microbiológica de silagens dos capins tanzânia e marandu acrescidas de polpa cítrica peletizada

O experimento foi conduzido com o objetivo de avaliar a dinâmica fermentativa e microbiológica de silagens de capins tropicais acrescidas de polpa cítrica. Os capins tanzânia (Panicum maximum cv. Tanzânia) e marandu (Brachiaria brizantha (Hochst ex. A. Rich) Stapf cv. Marandu) foram colhidos aos 64 e 49 dias de rebrota, respectivamente, e ensilados com 0, 5 ou 10% de polpa cítrica peletizada (PCP), em relação à matéria verde, durante 1, 4, 7, 14, 21, 28 e 56 dias. Foram utilizados silos experimentais de PVC adaptados com válvula do tipo Bunsen para eliminação dos gases. A forragem foi compactada visando obter densidade de 550 kg/m³. O delineamento utilizado foi o inteiramente ao acaso com três repetições, em esquema de parcelas subdivididas. A inclusão de PCP aumentou os teores de MS e diminuiu o pH das silagens. A adição de PCP influenciou os teores de N-NH3 (N total), uma vez que, nas silagens sem PCP, os teores N-NH3 foram significativamente elevados, o que as caracteriza como de qualidade duvidosa. A adição de PCP aumentou a concentração molar dos ácidos acético e propiônico. A população de enterobactérias foi detectada somente no primeiro dia de fermentação nas silagens do capim-tanzânia e até o 18º dia nas do capim-marandu. Nas silagens avaliadas, a população de bactérias homofermentativas foi semelhante à das bactérias heterofermentativas.

Digestibilidade da Matéria Seca, Proteína Bruta e Energia Bruta da Silagem de Milho associada ao Concentrado, por meio de ensaios in vivo e in vitro

A study was made to compare dry matter, crude protein and gross energy digestibility of corn silage, associated to concentrate, through in vitro and in vivo digestion techniques. A completely randomized design was used, with two treatments and nine replications, involving three assays. The in vivo digestion assay was conducted with 12 Holstein heifers, on a 24 h permanent sample collection. The in vitro digestion assay was achieved with three collection methods: manual (M), vacuum pump (VP) and nasoesophagic (N). The collection methods VP and M can he used to determine the dry matter digestibility, instead of in vivo method, for the present study ration. The digestion methods influenced the DM, CP and GE digestibility for the studied ration.

Digestibilidade e balanço de nitrogênio em ovinos alimentados à base de dietas com elevado teor de concentrado e níveis crescentes de polpa cítrica peletizada

O experimento foi realizado com o objetivo de determinar os coeficientes de digestibilidade, a ingestão de nutrientes e o balanço de nitrogênio de dietas com 20% de silagem de milho e 80% de concentrado e 0, 25, 40 e 55% de polpa cítrica na matéria seca total, substituindo o milho em grão. em delineamento de blocos ao acaso, foram utilizados oito cordeiros mestiços, com nove meses de idade e 34 kg de peso, mantidos em gaiolas individuais com dispositivo para separação de fezes e urina. O período de coleta de alimento, sobras, fezes e urina foi de seis dias e a quantidade de alimento oferecido correspondeu à média do consumido nos três últimos dias do período de adaptação. O experimento foi desenvolvido em duas fases, utilizando-se os mesmos animais, que foram distribuídos em blocos pelo peso. Os resultados foram analisados por regressão polinomial. Houve aumento linear nos coeficientes de digestibilidade aparente da proteína bruta e da fibra em detergente ácido, com o aumento da participação da polpa cítrica na dieta. Os demais coeficientes de digestibilidade não diferiram entre si e foram, respectivamente: 71,8; 73,3; 77,2; 63,5; e 72,2%; para matéria seca, matéria orgânica, extrato etéreo, fibra em detergente neutro e hemicelulose. O teor médio de nutrientes digestíveis totais foi de 72,39%. Houve aumento linear da ingestão de matéria seca e de nutrientes digestíveis totais por dia e por peso metabólico, com o aumento de polpa cítrica na dieta. O mesmo ocorreu com a quantidade de nitrogênio ingerido, absorvido, urinário e retido. O aumento da participação da polpa cítrica peletizada até 55% da matéria seca da dieta, substituindo o grão de milho, implicou em melhor aproveitamento da fibra e eficiência no metabolismo do nitrogênio.

Efeito da metionina protegida e não protegida da degradação ruminal sobre a produção e composição do leite de vacas holandesas

Utilizaram-se vacas Holandesas com produção superior a 20 kg de leite/dia, de primeira e segunda lactações, com 19±6 dias em lactação, para avaliar o efeito da suplementação com 8,4 g/dia de metionina protegida (MPDR) ou 8,4 g/dia de metionina não-protegida da degradação ruminal (MNPDR) sobre a produção e composição do leite, comparativamente a vacas controle, durante 90 dias. As vacas foram alimentadas com ração completa constituída por silagem de milho e concentrado. Produção de leite, teor de proteína do leite e produção de proteína não foram afetados pela suplementação com MPDR. As produções médias de leite foram 27,70; 27,09 e 27,61 kg/dia; os teores médios de proteína, 2,83; 2,85 e 2,77%; e as produções de proteína do leite, 0,77; 0,76 e 0,79 kg/dia, respectivamente, para vacas controle, suplementadas com MPDR e MNPDR. O teor de gordura do leite foi de 2,39; 2,12 e 1,89% paras vacas suplementadas com MPDR, MNPDR e controle, respectivamente. A produção diária de gordura foi 0,57; 0,58 e 0,58 kg/dia e a produção diária de leite corrigido para gordura (3,5%), 21,25; 21,19 e 21,35 kg/dia, para os respectivos tratamentos controle, MPDR e MNPDR. A suplementação com MPDR não alterou a produção de leite, porém melhorou a sua composição no início da lactação.