No abstract

Ajuste do peso corporal de bovinos para condições fisiológicas e de alimentação ……………………………………………………………….

At birth, calves display an underdeveloped rumen that eventually matures into a fully functional rumen as a result of solid food intake and microbial activity. However, little is known regarding the gradual impact of pre-weaning diet on the establishment of the rumen microbiota. Here, we employed next-generation sequencing to investigate the effects of the inclusion of starter concentrate (M: milk-fed vs. MC: milk plus starter concentrate fed) on archaeal, bacterial and anaerobic fungal communities in the rumens of 45 crossbred dairy calves across pre-weaning development (7, 28, 49, and 63 days). Our results show that archaeal, bacterial, and fungal taxa commonly found in the mature rumen were already established in the rumens of calves at 7 days old, regardless of diet. This confirms that microbiota colonization occurs in the absence of solid substrate. However, diet did significantly impact some microbial taxa. In the bacterial community, feeding starter concentrate promoted greater diversity of bacterial taxa known to degrade readily fermentable carbohydrates in the rumen (e.g., Megasphaera, Sharpea, and Succinivribrio). Shifts in the ruminal bacterial community also correlated to changes in fermentation patterns that favored the colonization of Methanosphaera sp. A4 in the rumen of MC calves. In contrast, M calves displayed a bacterial community dominated by taxa able to utilize milk nutrients (e.g., Lactobacillus, Bacteroides, and Parabacteroides). In both diet groups, the dominance of these milk-associated taxa decreased with age, suggesting that diet and age simultaneously drive changes in the structure and abundance of bacterial communities in the developing rumen. Changes in the composition and abundance of archaeal communities were attributed exclusively to diet, with more highly abundant Methanosphaera and less abundant Methanobrevibacter in MC calves. Finally, the fungal community was dominated by members of the genus SK3 and Caecomyces. Relative anaerobic fungal abundances did not change significantly in response to diet or age, likely due to high inter-animal variation and the low fiber content of starter concentrate. This study provides new insights into the colonization of archaea, bacteria, and anaerobic fungi communities in pre-ruminant calves that may be useful in designing strategies to promote colonization of target communities to improve functional development.

Microbial communities play critical roles in the gastrointestinal tracts (GIT) of preruminant calves by influencing performance and health. However, little is known about the establishment of microbial communities in the calf GIT or their dynamics during development. In this study, next-generation sequencing was used to assess changes in the bacterial communities of the rumen, jejunum, cecum, and colon in 26 crossbred calves at four developmental stages (7, 28, 49, and 63 days old). Alpha diversity differed among GIT regions with the lowest diversity and evenness in the jejunum, whereas no changes in alpha diversity were observed across developmental stage. Beta diversity analysis showed both region and age effects, with low numbers of operational taxonomic units (OTUs) shared between regions within a given age group or between ages in a given region. Taxonomic analysis revealed that several taxa coexisted in the rumen, jejunum, cecum, and colon but that their abundances differed considerably by GIT region and age. As calves aged, we observed lower abundances of taxa such as ,, and with higher abundances of and in the rumen. The jejunum also displayed taxonomic changes with increases in and taxa in older calves. In the lower gut, taxa such as, , and decreased and S24-7, , and increased as calves aged. These data support a model whereby early and successive colonization by bacteria occurs across the GIT of calves and provides insights into the temporal dynamics of the GIT microbiota of dairy calves during preweaning development. The gastrointestinal tracts (GIT) of ruminants, such as dairy cows, house complex microbial communities that contribute to their overall health and support their ability to produce milk. For example, the rumen microbiota converts feed into usable nutrients, while the jejunal microbiota provides access to protein. Thus, establishing a properly functioning GIT microbiota in dairy calves is critical to their productivity as adult cows. However, little is known about the establishment, maintenance, and dynamics of the calf GIT microbiota in early life. In this study, we evaluated the bacterial communities in the rumen, jejunum, cecum, and colon in dairy calves across preweaning development and show that they are highly variable early on in life before transitioning to a stable community. Understanding the dairy calf GIT microbiota has implications for ensuring proper health during early life and will aid in efforts to develop strategies for improving downstream production.

The average productive lifespan is approximately 3 to 4 years in countries with high-producing dairy cows. This is much shorter than the natural life expectancy of dairy cattle. Dairy farmers continue to cull cows primarily for reasons related to poor health, failure to conceive or conformation problems prior to culling. These reasons may indicate reduced welfare leading up to culling. Improvements in health care, housing and nutrition will reduce forced culling related to these welfare reasons. However, productive lifespan has remained similar in decades, despite large improvements in cow comfort and genetic selection for the ability to avoid culling. On the other hand, genetic progress for economically important traits is accelerating within the last decade, which should slightly shorten the average economically optimal productive lifespan. A major driver of productive lifespan is the availability of replacement heifers that force cows out when they calve. The average productive lifespan could be extended by reducing the supply of dairy heifers, which would also have benefits for environmental sustainability. Improvements in culling decision support tools would strengthen economically optimal replacement decisions. In conclusion, major factors of the relatively short productive lifespan of dairy cows are welfare-related, but other economic factors like supply of heifers, genetic progress and non-optimal decision-making also play important roles.

Twenty-six comparative slaughter studies were used (n = 752 animals) and coded within each experiment by gender (431 bulls, 204 steers, and 117 heifers) and breed (447 Nellore and 305 Bos indicus and Bos taurus crossbreds) to develop equations to predict the efficiency of use of ME to NE for growth (kg) and ME to NE for maintenance (km). The retained energy (RE) was regressed on ME intake (MEI) available for gain using orthogonal regression to obtain the kg within each experiment. The estimated kg was regressed on RE as protein (REp) according to the following equation: kg = a/(b + REp). Gender and breed effects were not tested because of limited number of experiments. The km was estimated as the intercept of the following equation: HP = β0 × e((β1 × MEI)), in which HP is heat production, β0 and β1 are coefficients, and e is the natural logarithm. The ME for maintenance (MEm) was computed assuming MEI equals to HP at maintenance. The km was obtained using the stepwise procedure of a multiple regression including ADG, empty body gain (EBG), empty BW (EBW), EBW(0.75), kg, and energy content in the EBW. A random coefficient model, assuming a random variation for study effects, was used to test breed and gender effects to identify the best model to estimate km. The overall equation to predict kg was 0.327 (±0.142)/[0.539 (±0.317) + REp], with an R(2) of 0.963. The equation to predict km was 0.513 (±0.024) + 0.173 (±0.061) × kg + a × EBG, R(2) = 0.92, in which a = 0.100 (±0.021) for B. indicus or a = 0.073 (±0.021) for crossbreds. Our results indicated that B. indicus were more efficient to use ME for maintenance. We concluded that km can be predicted from kg and EBG and that B. indicus × B. taurus crossbreds can affect km. Furthermore, kg can be predicted from REp and neither gender nor crossbreeding (B. indicus × B. taurus) affected kg. Because our database consisted of Nellore and B. indicus and B. taurus crossbreds, it is necessary to further evaluate differences between B. taurus and B. indicus regarding the kg.

This study was conducted to evaluate the development of the mammary gland in Holstein heifers subjected to different dietary metabolisable protein (MP): metabolisable energy (ME) ratios. Twenty-five Holstein heifers (initial body weight (BW) 213±13·5 kg and initial average age 7·8±0·5 months) were divided into five treatments. The treatments were designed to provide MP:ME ratios equal to 33, 38, 43, 48, and 53 g of MP per Mcal of ME. All diets were formulated to have the same energy content (2·6 Mcal ME/kg dry matter). Actual MP:ME ratios were 36·2, 40·2, 46·2, 47·1, and 50·8 g MP/Mcal ME. The experiment was conducted in a randomised block design, while considering initial BW as a blocking factor to evaluate pre- and post-pubertal periods. Block effect was not observed for all variables evaluated; hence it was considered that the diets had the same influence both on pre- and post-pubertal phases. Dry matter and nutrient intake did not change between treatments, excepting protein intake and digestibility. Serum concentrations of insulin-like growth factor 1 increased linearly across treatments. Changes in the pixel brightness of mammary gland ultrasound images, which are associated with lipid content, were significantly influenced by MP:ME ratios in the diet of heifers that were subjected to accelerated growth rates. It is not recommended to use diets of less than 38 g MP/Mcal ME in diets to heifers allowed to gain more than 1 kg/d.

RESUMO -Foram conduzidos dois experimentos com o objetivo de avaliar os indicadores internos fibra em detergente neutro indigestível (FDNi) e fibra em detergente ácido (FDAi), obtidos por incubação in situ durante seis dias, e os indicadores externos óxido crômico (Cr 2 O 3 ), dióxido de titânio (TiO 2 ) e lignina isolada, purificada e enriquecida (LIPE ® ) em dois esquemas de coleta total de fezes (3 ou 5 dias) para estimativa da digestibilidade em bovinos. O delineamento experimental foi o de blocos ao acaso com parcelas subdivididas. No primeiro experimento, foram utilizadas cinco novilhas mestiças alimentadas com cana-de-açúcar com 1% de ureia/sulfato de amônio e concentrado (1% do peso vivo). Não houve diferenças entre as metodologias de coleta para a digestibilidade da matéria seca. Quando estimada utilizando-se FDAi, a digestibilidade dos nutrientes foi subestimada, mas, quando estimada utilizando-se FDNi e os indicadores externos (óxido crômico, dióxido de titânio e LIPE ® ), não diferiu significativamente daquela determinada por coleta total de fezes. No segundo experimento, foram utilizadas oito vacas em lactação alimentadas com silagem de milho e 4 kg de concentrado. Não houve diferença na digestibilidade da matéria seca entre os períodos de coleta. A digestibilidade dos nutrientes, quando estimada utilizando-se FDNi, foi superestimada, mas, quando estimada utilizando-se FDAi e os indicadores externos (óxido crômico, dióxido de titânio e LIPE ® ), não diferiu significativamente daquela determinada por coleta total de fezes. Três dias de coleta são suficientes para estimativa da digestibilidade e os indicadores testados são eficientes na determinação da digestibilidade. Palavras-chave: coleta total, indicadores externos, indicadores internos Evaluation of markers in ruminant trials: digestibilityABSTRACT -Two studies were carried out to evaluate indigestible neutral detergent fiber (iNDF) and indigestible acid detergent fiber (iADF) as internal markers obtained by 144-h incubation in situ and chromium oxide (Cr 2 O 3 ), titanium dioxide (TiO 2 ) and isolated, purified and enriched lignin (LIPE ® ) as external markers, and two total fecal collection schemes (3 or 5 days) to estimate digestibility in bovines. The experimental procedure was a randomized block design in a split plot arrangement. In the first trial, five crossbreed heifers fed sugar cane plus 1% of urea/ammonium sulfate and concentrate (1% of body weight) were used. There was no difference for dry matter digestibility when the collection schemes were compared (5 days vs 3 days). The nutrient digestibility estimated by iADF was underestimated and those estimated by iNDF, chromium oxide, titanium dioxide and LIPE ® , did not differ from the digestibility calculated on total fecal collection. In the second trial, eight lactating cows fed corn silage and concentrate (4 kg/cow/day) were used. There was no difference for dry matter digestibility when the collection schemes were compared (5 days vs 3 days). The nutrient digestibility estimated by ...