Studio e monitoraggio del processo digestivo della bovina da latte finalizzato all’ottimizzazione dell’efficienza alimentare

Abstract

Nowadays, efficiency is a hot topic due to its link with farm profitability and environmental impact. The efficiency of dairy cows can be improved increasing both digestive and metabolic efficiency. The efficiency of digestion is affected by the characteristics and composition of feeds and diet but also by the degradative potential of the rumen and intestine that in turn is connected to adaptation processes and to the genetic potential of the animal. Digestion efficiency can be estimated through the combined evaluation and analysis of diet and faeces. Moreover, it can be monitored and evaluated by several tools and methods describing the function of the whole digestive tract. Within these tools I focused on the rumen fluid and faeces enzymatic activities as microbial activity reflection and expression as well as on the faeces chemical and physical evaluation. Some microbiome test was also performed on rumen fluid. The faeces chemical evaluation was performed to understand the exploitation of fibrous residues during the digestion process; the physical evaluation was instead performed to explore the possible relationship between particle size distribution and total tract dry matter and neutral detergent fiber digestibility. Related to the topic of feeds and supplements characteristics and effects on the digestion process, some results were reported on the effects of different carbohydrate sources on rumen fermentation processes and efficiency; moreover, an experiment was conducted to evaluate different slow-release urea prototypes demonstrating their low ammonia release compared to urea, mainly due to the different coating composition. Concerning the study of the ruminal and faecal enzymatic activities, the radial enzyme diffusion method was adapted to the study of these substrates and validated for amylase, cellulase and xylanase. Accuracy, precision, selectivity, sensitivity were tested and calibration curves were generated to express results as enzymatic concentration. The method resulted to be precise and accurate for all the enzyme if expressed as area of the halo, whereas the conversion to concentration reduced accuracy and precision, indicating the need for further studies on the calibration curves and interferences. After the validation the method was applied in different trials. An experiment was performed with the aim of evaluate the rumen fluid degradative potential evolution –studied in rumen fluids of different origin- during a priming procedure aimed at the standardisation of the in vitro digestibility tests. The RED method was able to describe the enzymes expression at the different interval tested. After a peak of activity in the first hours of incubation the amylase and xylanase reached the minimal differences at 8 hours of incubation, while cellulase was similar between different rumen fluid after 24 hours of incubation. The same method was applied to quantify the enzymatic activity variability connected to different diet typologies, showing the ability of the method in detecting the effects on the derived rumen fluids. Furthermore, individual, daily and weekly fluctuations of rumen degradative potential were tested in comparison with microbiome and VFA fluctuations. The use of RED highlighted the detection of individual differences in the rumen fluid degradative potential which were not detectable with both VFA and microbiome analysis in the short term. Moreover, the RED method appeared more practical, cheap and simple if compared to the microbiome tests. Concerning the fecal evaluation several experiment have been performed to: (a) validate the set of sieves composed by screens of 0.15, 0.6, 1.18, 2.36 and 4.5 mm pore sizes; (b) assess the relation between the rumen fluid degradative capacity and the digestion efficiency; (c) evaluate the degree of exploitation of the fecal particle residues on each sieve, to understand which one is more related to the digestion process of lactating dairy cows. The set of sieves for fecal evaluation can be an easy and cheap method to analyse the digestion efficiency. Due to the ability of the undigestible fractions in the estimation of the total-tract apparent digestibility of nutrient, it has been determined the uNDF of the diet and feces to estimates apparent total-tract digestibility of dry matter (ttaDMDe) and neutral detergent fiber (ttaNDFDe). The results on the validation of the set of faecal sieves suggested to remove the screen 1 (4.5 mm pores). Faecal particles retained in the 1.18 mm screen and 2.36 mm were the most exploited containing the lowest digestible dry matter residue while this range is wider for the residual potentially digestible fibre. The total proportion of faecal particles retained on the 1.18 mm screen are highly correlated with the estimated total tract apparent DMD while the total proportion of faecal particles retained on the 0.6 mm screen are highly correlated to the estimated apparent total-tract NDFD. The faecal sieving can be performed using only the 1.18, 0.6 and 0.15 mm screen for farm evaluation. Whereas, further study on the retained particles composition need to be performed. A further study has been performed to test the ability of the faecal near infrared spectroscopy (FNIRS) to estimate the uNDF240 and other fiber fractions in faeces of lactating dairy Holstein cattle. The FNIRS is a cheap and fast method to perform several analyses; conversely, the determination of the uNDF is time consuming. Consequently, uNDF prediction through this instrument has a strong interest. The prediction models are not very accurate, however, this trial contributes to the knowledge of the FNIRS application to uNDF240 and other fibre fractions in faeces.