Citrus Pulp as an Alternative Energy Source for High-Yielding Dairy Cows in Tropical Systems: Effects on Intake, Digestibility, Nitrogen Balance, and Dairy Performance.

Carbohydrates are the most abundant biomolecules in nature and account for 70 to 80% of ruminant diets. Among the classifications, non-fibrous carbohydrates have been commonly used to increase milk production. Thus, the objective of this study was to evaluate the effects of the use of non-fibrous carbohydrates (NFC), such as cornmeal, pre-gelatinized corn, citrus pulp and sucrose, on nutrient intake, digestibility, milk yield and composition in lactating dairy goats. Twenty-nine primiparous (11) and multiparous (18) lactating Saanen and Alpine goats (2.8 ± 0.27 kg.d-1 milk; 55.4 ± 1.8 kg body weight) were used in this study. The goats were distributed in eight pens with four animals each, with the pen being the experimental unit and the animals being the observational units, and in four diets in a 4×4 balanced double Latin square design, with four periods of 21 days each. During the first period of the experiment, three goats stopped producing milk and were removed from the experiment. The treatments were corn meal, pre-gelatinized corn, citrus pulp and sucrose, with the roughage based on corn silage, and the roughage:concentrate ratio 60:40. The diets were formulated to meet the nutritional requirements of lactating goats and were offered in four daily meals, in the same physical form. Voluntary nutrient intake, digestibility, production weighing and samples for analysis of milk composition were performed during the seven days of each collection period. We did not consider the effect of body weight, due to the short evaluation periods present in the Latin square design, which tend to hinder the variation of weight gain, not correcting errors in ruminal filling. Goats fed corn meal showed higher lignin intake and digestibility of dry matter, organic matter and fiber, and lower intake when sucrose was used. Citrus pulp also stood out for its fiber digestibility and influenced some milk components, such as fat, protein, total solids, milk fat-corrected and net lactation energy. However, milk composition showed low values when the goats were fed sucrose. Regarding the period, only fat, milk fat- corrected and net lactation energy were influenced. Regarding ingestive behavior, there was an influence of the diet for intake, being greater when the goats received corn meal and smaller when they received pre-gelatinized corn. Regarding idleness, we observed the opposite effect, being greater in the pre-gelatinized corn diet and smaller with corn meal in the diet. We suggest that citrus pulp can be used as a concentrated feed for dairy goats, without compromising nutrient intake, digestibility, milk yield and composition. However, diets with sucrose affect intake, digestibility, milk production and composition. Keywords: Citrus pulp. Digestibility. Milk production. Sucrose

This thesis offers a solution for protein deficiency in human diets of rural people in developing countries. Dairy goats can provide locally produced protein rich foods. However, the low production of goats in these countries is often owing to low dietary intake of nitrogen and energy associated with low quality feeds. A combination of a cheap nitrogen (N) source and a readily available dietary energy source such as grain has been suggested to improve the productivity of milking goats. The purpose of this thesis work was to determine if the amount and type of dietary N, and the ratio between N and available energy in the diet are important for enhancing milk protein and production in dairy goats. In the first three feeding trials, the effects of feeding barley meal supplemented with either soybean meal (SBM), cottonseed meal (CSM) or urea on nutrient intake, nutrient digestibility, nitrogen balance (NB), microbial nitrogen synthesis (MNS), growth rate and milk protein and production were investigated using cross-bred (Anglo Nubian x Angora) growing goats and milking Saanen goats. There were no significant differences in hay intake, metabolizable energy (ME) intake, growth rate, nitrogen balance (NB), total ruminal volatile fatty acid (VFA) concentration, MNS and efficiency in growing dairy goats offered different dietary nitrogen sources, although the digestibility of nutrients was significantly (P< 0.01) improved. Nitrogen balance was significantly affected by N supplementation for milking goats, but the total nutrient intake, nutrient digestion, milk-feed efficiency, milk protein and production were not affected. In experiment 4, milking Saanen goats were used to examine whether increasing the levels of N in the isocaloric diets could enhance nutrient digestibility, NB, milk protein and yield. No improvement was observed in nutrient intakes, milk-N and production, milk-feed efficiency, digestibility of dry matter (DM), organic matter (OM), neutral detergent fibre (NDF) and energy (DE) and NB. Digestible organic matter intake (DOMI) had more effect on milk production than dietary N intake. Any excess of dietary N was excreted in the urine. There was no benefit in feeding dairy goats a diet containing more than 2.4% N (15.3% protein). The nutrient complementary effects of nitrogen sources for the goats did not affect N metabolism presumably because the energy content of the diet was the limiting factor. In experiment 5, milking Saanen goats were offered nine combinations of dietary urea (Ul= 0 g, U2= 80 g, U3=160 g) and energy (El= 1000 g, E2= 1200 g, E3= 1400 g barley meal) supplements. The goats were fed a basal diet of barley straw. Increasing dietary urea and readily available dietary energy did not significantly increase milk protein and milk yield, milk production efficiency or the total nutrient intakes or digestibility. Some combination of urea and readily available energy level gave significant responses. The U1E3 and U2E3 improved milk yield; U2E1 and U3E1 improved straw intakes; U2E2 and U3E3 improved nutrient digestibility. The U1El treatment gave significantly lower rates of MNS than other combination treatments. The highest rate of MNS was recorded in goats fed the U2U3 treatment, although this response was not statistically significant. Significant relationships were observed between rate of MNS and digestible organic intake (DOMI) (r = 0.73; P<0.0001), gross energy intake (GEI) (r = 0.67; P<0.0001) and digestible energy intake (DEI) (r = 0.59; P<0.0001). The relationship between MNS and N intake was slightly weaker (r=0.55; P<0.0001). However, no relationship was observed between MNS and total VFA, rumen ammonia-N, or plasma urea concentration. The daily MNS in dairy goats could be estimated using either of these following equations: MNS (g/day) = 1.16 + 0.046 DOMI (g); (R2= 0.73; P<0.0001). Or MNS = 0.116 + 0.996 GEI + 0.005 GEI x NX (R2 = 0.78 and P< 0.0001). It was concluded that the total ruminal VFA and ammonia-N concentration were responsible for the response of milking goats to the dietary supplement. Also of important was the synchronisation of the diumal mminal ammonia-N concentration with the diurnal variation of readily available energy. Overall, the results suggest that urea is as good as soybean meal and cottonseed meal for growing and milking goats if sufficient dietary energy is readily available. However, to prevent ammonia loss from urea before it can be incorporation into microbial N, the intake of fermentable carbohydrate must be sufficient. Thus, urea remains a promising source of N for improving the production of milk from goats in developing countries. The effectiveness of dietary urea supplementation is dependent upon the concurrent supplementation of the diet with readily available energy sources. Urea plus grain supplementation is effective and cheaper than providing dietary amino-protein sources to milking goats.

Effect of replacing ground corn and soybean meal with licuri cake on the performance, digestibility, nitrogen metabolism and ingestive behavior in lactating dairy cows

Feed intake and milk production in dairy cows fed different grass and legume species: a meta-analysis

The present study aimed at assessing the effects of hepatoprotective agents in diets that contain sources of energy on milk production, milk composition, and nutrient partition in lactating cows. Sixteen Holstein x Gir crossbred mid-lactation cows with an average body weight of 553 ± 85 kg were used in this study. These animals were allocated in a 4x4 Latin square design. A 2x2 factorial arrangement was employed in this feeding experiment. In each treatment, cows received diets with or without a hepatoprotective agent and variable in ground corn grain or citrus pulp as energy sources. Evaluated parameters included nutrient intake and digestibility, milk production, milk composition, energy balance, and nitrogen balance. Performance and nutrient balance variables were assessed and no interaction was observed between the hepatoprotective compounds and the dietary sources of energy. Dry matter intake, milk production and net energy for lactation were higher in corn as an energy source whereas milk fat content was higher in citrus pulp diets. There was a reduction in protein and casein contents in the milk of cows that was supplemented with an hepatoprotective agent. In this study, the hepatoprotective agent improved nitrogen balance in dairy cows. The use of the hepatoprotective compounds in the diet of these lactating cows in confinement reduced the milk protein fraction and favored a higher nitrogen balance in these animals. Retention of nitrogen compounds in the metabolism of lactating cows under confinement is influenced by hepatoprotective agents.

Objetivou-se avaliar níveis de concentrados energéticos e proteicos sobre o desempenho de vacas leiteiras Holandês x Zebu, com peso corporal de 452±77kg, de terceira e quarta lactação, 80 dias pós-parto e produção de 12,8kg de leite/dia. Nove vacas foram distribuídas em três quadrados latinos 3x3, em períodos experimentais de 10 dias, distribuídas segundo número de lactações, sendo os tratamentos níveis de farelo de soja (FS) em substituição ao fubá de milho (FM) (0,8; 1,6 e 2,4kg/vaca dia, completando para 3,2kg/vaca dia com FM), níveis de FS ou de FM (0,8; 1,6 e 3,2kg/vaca/dia) e silagem de milho como volumoso. Somente o consumo de proteína bruta se elevou com o aumento nos níveis de FS em dietas contendo FM+FS, ao passo que os consumos diários de matéria seca (MS) e das frações nutricionais aumentaram com a elevação do FS ou FM. Os coeficientes de digestibilidade da MS e dos nutrientes não diferiram em dietas contendo FM+FS. A digestibilidade da proteína bruta (PB) aumentou ao passar de 1,6 para 3,2kg/dia de FS. Houve diminuição da digestibilidade da MS, MO e CNF ao passar de 0,8 para 3,2kg/dia de FM e diminuição do NDT ao passar de 1,6 para 3,2kg/dia de FM. As exigências de NDT e PB só foram satisfeitas plenamente com 0,8+2,4kg (FM+FS) e 3,2kg de FS. As dietas contendo FM não atenderam sequer às exigências de NDT. A produção de leite e a sua composição bem como o peso corporal e a eficiência alimentar relacionada ao CMS não foram influenciados pelos tratamentos. A eficiência alimentar em relação ao fornecimento de concentrado decresceu quando se adicionaram níveis crescentes de FS ou FM. Tendo como volumoso a silagem de milho, o fornecimento de fubá de milho ou farelo de soja, nas quantidades analisadas neste experimento, não promove aumento da produção de leite ou de seus constituintes, sendo que a eficiência do uso do concentrado diminui ao se elevar o nível de suplementação.

The objective of this study was to explore the effects of corn silage, alfalfa hay, and oat-vetch mixed silage combinations on milk production, rumen fermentation, nutrient digestibility, and feeding cost in dairy cows. Nine multiparous Holstein dairy cows (DIM: 94.11 ± 9 d, milk yield: 41.0 ± 2.5 kg) were each fed 3 experimental diets in a replicated Latin square design. The experimental diets contained corn silage, alfalfa hay, and mixed silage in 3 different forage proportions (diet 1, 40:10:0; diet 2, 30:5:15, and diet 3, 20:0:30; DM basis). Cotton seed meal (CSM) or soybean meal (SBM) were used as the protein source to balance the CP content. The mixed silage was made from oats and vetch grown together in a 50:50 ratio, and all diets were formulated to contain 16% CP and 50:50 forage-to-concentrate ratio (DM basis). Cows fed diet 3 had a 9% reduction in DMI compared with diet 1. Associated with this reduction in DMI, cows fed diet 3 also had reduced yield of milk protein (22.0%), fat (15.7%), and lactose (18.5%) compared with cows fed diet 1. Characteristics of rumen fermentation were similar among diets; however, cows fed diet 3 had lower rumen fluid valerate and higher acetate: propionate ratios compared with diet 1. The N intake was not different among cows fed the 3 diets, but cows fed diet 3 excreted 0.2% less urinary N compared with diet 1. The combinations of corn silage and mixed silage reduced the cost of the diets (diet 1, $0.543; diet 2, $0.503; diet 3, $0.465/kg DM), and whereas milk production was reduced, the feed cost per milk yield was lowest for cows fed diet 3 ($0.404) and highest for cows fed diet 1 ($0.407). We conclude that cows fed diets with combinations of corn silage, alfalfa hay, and mixed silage, consumed less feed and produced less milk but also produced less urinary N and had a lower cost of feed for milk production than cows fed corn silage diets. This demonstrated that partial displacement of expensive corn silage, alfalfa hay, and SBM with mixed silage and CSM reduced costs, but due to the reduced DMI and milk yields, more research on these diets will be needed before they can be recommended as viable options to replace corn silage and SBM diets.

Until recently, young, highly digestible grass was considered an ideal feed for dairy cows. However, research during the last decades has shown that the nutrient supply of grazing animals is insufficient for milk productions above c. 29 kg per day. Experiments in England and New Zealand have shown that the efficiency of protein utilization is relatively low and consequently, a high proportion of ingested nitrogen is excreted in urine and faeces. This reports the effects of grassland management and feeding strategies on the digestion and availability of nutrients from perennial rye- grass ( Lolium perenne ) in dairy cows.Chapter 1 is a literature review of the various factors affecting the composition and nutritional quality of grass. To facilitate high yields of dry matter and a high feeding value, grass is fertilized with high levels of nitrogen. Level of nitrogen fertilization, weather conditions and the duration between nitrogen application and harvesting date affect the content and quality of grass protein. Level of nitrogen fertilization and maturity also influence other components of grass, like carbohydrates and lipids.In Chapter 2 it is emphasized that high levels of nitrogen fertilization result in high concentrations of crude protein, which are easily fermented in the forestomachs. Thus, in grazing dairy cows, an important part of grass protein is fermented in the rumen and subsequently excreted in the urine. The actual efficiency of nitrogen utilization in cows grazing intensively managed pastures, is 15 to 25 %. We estimated that theoretically a 600 kg cow producing 25 kg milk per day can utilize dietary nitrogen with a maximum efficiency of 40 to 45%. This chapter discusses changes in grassland management and nutrition aiming at improvements of nitrogen utilization. When grass is the sole feed, efficiency of nitrogen utilization cannot be improved substantially without have a detrimental effect on animal performance. Supplementing the diet of grazing dairy cows with low protein, high energy feeds increases the efficiency of nitrogen utilization, mainly because it reduces nitrogen intake.Chapters 3 and 4 contain details of experiments using the nylon bag technique. Chapter 3 discusses the effects of grass maturation and rate of nitrogen fertilization on rumen degradability of organic matter and crude protein in fresh grass. These results were used to estimate the content of digestible protein entering the small intestine. Crude protein content and in situ degradability of organic matter and crude protein decreased with increasing grass maturity and with decreasing nitrogen application. With every 100 g per kg dry matter decrease in crude protein content, the estimated content of digestible protein entering the small intestine decreased by 19 g per kg dry matter, irrespective of how the crude protein content was manipulated.Chapter 4 discusses rumen degradability of crude protein and non-protein organic matter (- carbohydrates) of fresh and preserved grass, obtained in four nylon bag studies, and consequences for dairy cow rations. In Experiment 1, the effect of level of fertilization on the in situ degradation of fresh grass was studied. The second experiment focused on the effect of maturation on degradation of fresh grass. Experiments 3 and 4 dealt with the influence of maturation and dry matter content of grass silage and hay. Experiment 4 also included treatment with cell wall degrading enzymes. Fresh and preserved grass fertilized at high levels of nitrogen, contained large surpluses of fermentable nitrogen. In fresh grass the ratio of [soluble nitrogen]:[soluble carbohydrates] was lower than the ratio of [insoluble, degraded nitrogen]:[insoluble, degraded carbohydrates]. Therefore, it was concluded that ingredients with a low ratio of [insoluble, degraded nitrogen]: [insoluble, degraded carbohydrates] may be considered appropriate supplements to grass-based diets. In preserved grass the ratio of [soluble nitrogen]:[soluble carbohydrates] exceeded the ratio of [insoluble, degraded nitrogen]:[insoluble, degraded carbohydrates]. Wilting had no consistent effect on the [nitrogen]:[carbohydrates] ratio. Treatment with cell wall degrading enzymes resulted in a lower [soluble nitrogen]:[soluble carbohydrates] ratio. From these results it was concluded that silage-based diets require supplementation with ingredients rich in soluble carbohydrates.Chapter 5 reports an experiment in which the digestion and intestinal amino acid supply were studied in three rumen and duodenal cannulated lactating cows fed freshly cut grass. Grass was fertilized at levels of 275 or 500 kg of nitrogen/ha per year. High-nitrogen grass was fed in June and October; low-nitrogen grass in July and September. When low-nitrogen grass was fed, the digestibilities of organic matter and crude protein were lower than found with high-nitrogen grass. On low-nitrogen grass, the duodenal nitrogen flow expressed per unit of nitrogen intake was higher. The flow of amino acid nitrogen on low-nitrogen grass was slower in September, mainly because of reduced microbial protein synthesis attributed to slower organic matter degradation of low-nitrogen grass. Duodenal nitrogen flow per unit of nitrogen intake was inversely related to the nitrogen: organic matter ratio of the diet. Rate of nitrogen fertilization did not affect ruminal turnover of organic matter and neutral detergent fibre. Turnover and passage rates recorded in this experiment did not differ from reported data on cows fed winter rations at similar levels of dry matter intake.Changes observed in vivo in digestion and amino acid supply when fresh grass was partly replaced by concentrate mixtures (either maize starch or sugar beet pulp fibre) are presented in Chapter 6. Partial replacement of grass decreased crude protein digestibility. When high starch concentrate was fed, overall digestibility of neutral detergent fibre was lower than on the high fibre diet, mainly because of decreased ruminal digestion of neutral detergent fibre. With the high starch concentrate, 39% of the ingested starch escaped ruminal fermentation. Although less organic matter was fermented in the forestomachs on high starch concentrate, the duodenal amino acid nitrogen flow was higher than on the high fibre concentrate. The proportion of microbial protein was unaffected; thus, efficiency of microbial synthesis was estimated to be higher when high starch concentrate was fed.In the experiment reported in Chapter 7, six grazing dairy cows each fitted with a rumen cannula, were supplemented with high or low starch concentrates. The cows received 1 kg or 7 kg of high or 7 kg of low starch concentrate in two equal meals per day fed after milking. After a three-week adaptation period, samples were taken of grass and rumen fluid. Total sugar content of grass increased during daytime with the highest concentration directly before sunset. Patterns of ruminal pH values did not differ between treatments and were minimal at midnight. Volatile fatty acids and ammonia peaked at midnight. Supplementation with 7 kg of concentrate decreased rumen concentrations of ammonia and branched-chain volatile fatty acids. Acetate: propionate and non- glucogenic:glucogenic ratios of volatile fatty acids and percentage of milk fat tended to be lowest when the diet included 7 kg of high starch concentrate.Chapter 8 describes three ruminal fermentation studies carried out in combination with three feeding trials. These experiments were carried out to investigate the effect of partial replacement of grass by low protein feedstuffs on pH and concentrations of volatile fatty acids and ammonia in the rumen and on nitrogen excretion in milk, urine, and faeces by dairy cows. Feedstuffs tested were the high-starch and high-fibre concentrates used in the experiment reported in Chapter 6, maize silage, dried and ensiled pressed sugar beet pulp and high-moisture ear maize silage with or without husks. Partial replacement often increased dry matter intake, resulting in minor effects on nitrogen intake. Urinary nitrogen excretion ranged between 30 and 58% of nitrogen intake and decreased by 30 to 40% when grass was partially replaced. The reduction in urinary nitrogen excretion corresponded to a decrease of rumen ammonia. Faecal nitrogen output ranged between 25 and 30% of nitrogen intake and tended to increase with inclusion of low protein feed. Replacement by concentrate mixtures based on maize reduced milk fat content without changing rumen volatile fatty acid composition; for mixtures based on beet pulp, milk fat content remained unaffected.In the General Discussion (Chapter 9), the supply of aminogenic, glucogenic and ketogenic nutrients from grass is estimated from the obtained data. Supply of nutrients depends on total dry matter intake and on the composition of the dry matter.From the rumen evacuation data it was concluded that rumen fill is not a factor limiting grass intake. Possible limiting factors are discussed, like fermentation products (ammonia, volatile fatty acids) and the maximum capacity in chewing activity (grazing and ruminating).Relationships between crude protein content and the proportion of protein escaping from rumen fermentation were used to predict the supply of available protein in the small intestine. A curvilinear relationship was found between crude protein and predicted amount of available protein. Extrapolation suggested that a plateau level of c. 125 g available protein (DVE) per kg dry matter is reached at crude protein concentrations above 270 g per kg dry matter. This was higher than concluded in Chapter 5 from the in vivo results, where a maximum duodenal non-ammonia nitrogen flow was predicted when grass contains 225 g crude protein per kg dry matter. The nitrogen losses in the rumen increased linearly with crude protein content.The predicted supply of available protein based on in situ data agreed with in vivo data for grazing steers reported in literature, but was higher than the duodenal protein flow in dairy cows observed in our experiments. This discrepancy was mainly attributed to the low efficiency of microbial protein synthesis estimated in our experiments. Possible explanations discussed included the higher intake level and higher proportion of soluble carbohydrates and proteins in grass observed in our experiments compared to those reported in steers. Differences may also result from methodological errors. It was estimated that cows consuming 16 kg of grass organic matter and producing 27 kg of milk per day are in a large positive balance of glucogenic and ketogenic nutrients. However, comparing nutrient and energy requirements showed that the assumed nutrient requirements for maintenance and milk production are too low, whereas the nutrient supply was overestimated.An estimate was made of the effect of a decrease in nitrogen content in grass on the flow of nitrogen in grazing dairy cows, using a simplified model. Decreasing the nitrogen content in grass reduced nitrogen excretion in urine and faeces concomitant with an decrease in the proportion excreted in urine.The model was also used to predict the effects of partial replacement of grass by low protein concentrates. This resulted in a reduction in urinary nitrogen excretion with only minor changes in faecal nitrogen output. The efficiency of nitrogen utilization increased.It was concluded that the crude protein content in grass can be reduced to concentrations of c. 225 g per kg dry matter without significant negative effects on the supply of aminogenic nutrients. Yet even at that level, urinary ruminal and metabolic nitrogen losses will be significant. Since further decrease in protein content is correlated to a reduction in dry matter yield and in the nutritive value of grass, a further reduction of nitrogen losses should be established by partial replacement of grass by low protein feeds.

This study aimed to evaluate the effect of diets containing sunflower or corn silages and concentrate based on citrus pulp or ground corn on intake, apparent digestibility, feeding behavior, microbial protein production, and production, composition, and fatty acid profile of milk from dairy cows. Eight multiparous lactating Holstein cows (586±61 kg live weight; 25.0±4.0 kg daily milk yield at 80 to 120 days in milk) were randomly assigned to a double 4 × 4 Latin square design with a 2 × 2 factorial array. The experimental diets were: sunflower silage + citrus pulp-based concentrate; sunflower silage + ground corn-based concentrate; corn silage + citrus pulp-based concentrate; and corn silage + ground corn-based concentrate. The dry matter intake was highest for diets containing sunflower silage and lowest for diets with citrus pulp. Sunflower silage provided the highest intakes of crude protein, neutral detergent fiber, and ether extract. Except for the ether extract, the type of forage and carbohydrate did not influence the apparent nutrient digestibility. The forage and carbohydrate sources did not influence the feed eating time, but animals fed sunflower silage showed decreased rumination time and chewing activity. The microbial protein production was not altered with the diets. No differences were observed for milk production or composition, except for the milk urea nitrogen and lactose concentration. The type of forage influenced the milk fatty acid profile, to which corn silage presented higher values for fatty acids up to a 17-carbon chain length. The inclusion of sunflower silage and citrus pulp, compared with corn silage and ground corn, alters dry matter intake and ingestive behavior, but maintains milk production and composition with satisfactory characteristics of the milk fatty acid profile, providing an alternative feed for dairy cows.

Effects of substitution of barley with citrus pulp on diet digestibility and intake and production of lactating ewes offered mixed diets based on ammonia-treated barley straw

The chemical characteristics of Cenchrus clandestinus grass, nutritional base in dairy production systems, demand the energy supplementation. Corn grain is the most used food for this purpose, but considering its demand and prices, the objective of this work was to evaluate its partial replacement by alternative non-fibrous carbohydrates sources on methane emissions, energy and nitrogen balance and productive performance of dairy cows. Sixteen multiparous Holstein cows were fed Cenchrus clandestinus plus one of four concentrate supplements formulated with corn (Zea mays) or a partial replacement of corn with sorghum (Sorghum vulgare), cassava (Manihot esculenta) or citrus pulp (Citrus sp.). Inclusion of sorghum, cassava or citrus pulp did not affect dry matter intake, dry matter digestibility, enteric methane emissions, energy and nitrogen balance, milk yield or composition. The results allow to conclude that these ingredients can partially replace corn in the diet of lactating dairy cows.

Increasing the concentration of linolenic acid in diets fed to Jersey cows in late lactation does not affect methane production

We evaluated the effect of three sources of dried distillers' grains with solubles (DDGS) in diets of mid-lactating dairy cows on milk production and milk composition and on digestibility in sheep. DDGS from wheat, corn and barley (DDGS1 ), wheat and corn (DDGS2 ) and wheat (DDGS3 ) were studied and compared with a rapeseed meal (RSM). RSM and DDGS were characterized through in situ crude protein (CP) degradability. Nutrient digestibility was determined in sheep. Twenty-four multiparous cows were used in a 4 × 4 Latin square design with 28-day periods. Treatments included total mixed rations containing as primary protein sources RSM (control), DDGS1 (D1), DDGS2 (D2) or DDGS3 (D3). RSM contained less rapidly degradable CP (fraction a), more potentially degradable CP (fraction b) and more rumen undegradable CP (UDP) than the three DDGS. In vivo digestibility of RSM organic matter was similar to DDGS. Calculated net energy for lactation (NEL ) was lower for RSM (7.4 MJ/kg DM) than for DDGS, which averaged 7.7 MJ/kg DM. Cows' dry matter intake did not differ between diets (21.7 kg/day). Cows fed D1 yielded more milk than those fed D3 (31.7 vs. 30.4 kg/day); no differences were found between control and DDGS diets (31.3 vs. 31.1 kg/day). Energy-corrected milk was similar among diets (31.2 kg/day). Diets affected neither milk fat concentration (4.0%) nor milk fat yield (1.24 kg/day). Milk protein yield of control (1.12 kg/day) was significantly higher than D3 (1.06 kg/day) but not different form D1 and D2 (1.08 kg/day each). Feeding DDGS significantly increased milk lactose concentration (4.91%) in relation to control (4.81%). DDGS can be a suitable feed in relation to RSM and can be fed up to 4 kg dry matter per day in rations of dairy cows in mid-lactation. However, high variation of protein and energy values of DDGS should be considered when included in diets of dairy cows.

Our objective was to evaluate the effects of dietary starch concentration on milk production, nutrient digestibility, and methane emissions in lactating dairy cows. Thirty mid-lactation cows were randomly assigned to either a high-neutral-detergent-fiber, low-starch diet (LS; 20.2% starch) or a low-neutral-detergent-fiber, high-starch diet (HS; 25.2% starch) following a 3-week acclimation. The study lasted 8 weeks, with milk sampling and gas measurements conducted weekly during acclimation and at weeks 2, 4, 6, and 8. Blood and fecal samples were collected during acclimation and week 8. Compared with LS cows, HS cows produced 1.9 kg/d more energy-corrected milk (4.45% increase), with higher yields of true protein (+0.13 kg/day), lactose (+0.10 kg/day), and total solids (+0.24 kg/day). Dry matter and organic matter digestibility was 4.2 and 4.3% higher, respectively, in the HS group. The milk fatty acid (FA) profile differed, with LS cows having greater mixed FA content and HS cows showing higher de novo FA content and yield. Although methane production tended to be higher in HS cows (+25 g/day), methane yield decreased by 8.8%. Overall, the HS diet improved milk production, nutrient digestibility, and environmental efficiency by reducing methane yield in dairy cows.

Concentrations of nutrients needed in the rations of high producing dairy cows are determined by the animals’ requirements and by their potential feed intake. As the genetic potential for milk production increases, it is more difficult to formulate rations with the required concentrations of energy. Energy density of rations can be increased by replacing forage with grains, however, this can lead to a multitude of digestive and metabolic problems like acidosis, rumen indigestion, bloat, reduced fibre digestibility, secretion of milk with low concentrations of fat, lameness and liver damage. Substitution of fat for a grain is a method of increasing energy density as fats have more than twice the energy density of grain. But, the main problem in using fats in dairy diets is that it depresses milk protein content which is important for the consumer and cheese manufacturers. This project was designed to further investigate the effects of fat supplementation of diets on diet digestibility and milk composition with a particular focus on milk protein content. The studies conducted were: 1. The effects of oilseed (whole cottonseed) supplementation on rumen function and microbial synthesis in sheep. 2. The effect of supplementing diets with soybean oil and different carbohydrate sources with different degrees of rumen solubility on milk production and composition in dairy cows. 3. The effect of post-ruminal infusion of soybean oil on food intake, milk production and composition of goats. 4. The effect of post-ruminal infusion of sodium caseinate and the amino acids lysine and methionine on milk production and milk composition of goats supplemented with soybean oil. In the first experiment seven sheep were fed three diets. The control diet had a roughage to concentrate ratio of 1:1. The other two had 15% and 30% of the concentrate energy replaced with whole cottonseed. The double marker method (Cr-EDTA and ytterbium chloride) was used to estimate flow rate of nutrients from rumen and S35 was used to estimate microbial synthesis. Despite repeating this experiment, the results obtained using the double marker technique were not satisfactory. Consequently, the flow rate of nutrients was calculated using a single marker (Cr-EDTA). No significant differences were found for extent of nutrient digestibility in the rumen or flow of nutrients from the rumen. However, there were significant differences for DM and NDF digestibilities in the total tract. The results of the study with dairy cows indicated that oil can replace or be fed with carbohydrate sources (grain or molasses) without any significant effect on milk production or composition. A combined supplement of sorghum, soybean oil and formaldhayde treated soybean meal gave the best performance by grazing dairy cows in mid lactation.