Effect of dairy farming system, herd, season, parity, and days in milk on modeling of the coagulation, curd firming, and syneresis of bovine milk

Abstract

The objectives of this study were to characterize the variation in curd firmness model parameters obtained from coagulating bovine milk samples, and to investigate the effects of the dairy system, season, individual farm, and factors related to individual cows (days in milk and parity). Individual milk samples (n = 1,264) were collected during the evening milking of 85 farms representing different environments and farming systems in the northeastern Italian Alps. The dairy herds were classified into 4 farming system categories: traditional system with tied animals (29 herds), modern dairy systems with traditional feeding based on hay and compound feed (30 herds), modern dairy system with total mixed ration (TMR) that included silage as a large proportion of the diet (9 herds), and modern dairy system with silage-free TMR (17 herds). Milk samples were analyzed for milk composition and coagulation properties, and parameters were modeled using curd firmness measures (CFt) collected every 15 s from a lacto-dynamographic analysis of 90 min. When compared with traditional milk coagulation properties (MCP), the curd firming measures showed greater variability and yielded a more accurate description of the milk coagulation process: the model converged for 93.1% of the milk samples, allowing estimation of 4 CFt parameters and 2 derived traits [maximum CF (CF(max)) and time from rennet addition to CF(max) (t(max))] for each sample. The milk samples whose CFt equations did not converge showed longer rennet coagulation times obtained from the model (RCT(eq)) and higher somatic cell score, and came from less-productive cows. Among the sources of variation tested for the CFt parameters, dairy herd system yielded the greatest differences for the contrast between the traditional farm and the 3 modern farms, with the latter showing earlier coagulation and greater instant syneresis rate constant (k(SR)). The use of TMR yielded a greater tmax because of a higher instant curd-firming rate constant (k(CF)). Season of sampling was found to be very important, yielding higher values during winter for all traits except k(CF) and k(SR). All CFt traits were affected by individual cow factors. For parity, milk produced by first-lactation cows showed higher k(CF) and k(SR), but delays in achieving CF(max). With respect to stage of lactation, RCT(eq) and potential asymptotic CF increased during the middle of lactation and stabilized thereafter, whereas the 2 instant rate constants presented the opposite pattern, with the lowest (k(CF)) and highest (k(SR)) values occurring in mid lactation. The new challenge offered by prolonging the test interval and individual modeling of milk technological properties allowed us to study the effects of parameters related to the environment and to individual cows. This novel strategy may be useful for investigating the genetic variability of these new coagulation traits.

Modeling of coagulation, curd firming, and syneresis of milk from Sarda ewes

“…The iterative estimation procedure applied to the 240 point measurements of 4.4% (49 of 1,121 ewes) of the milk samples for the estimation of the individual CF t model parameters did not comply with the required convergence criteria. An incidence of 6.8% (85 of 1,243 cows) has been recorded in a large survey on Brown Swiss cows (Bittante et al, 2015). In both cows and ewes, the nonconvergent samples were characterized by a physico-chemical composition similar to the convergent samples (Table 2) but had a larger RCT than the average value (+39% for ovine and +76% for bovine species) and especially of SD (+195% for ovine and +64% for bovine species).…”

“…If not-converged samples were characterized by an increase in RCT and a tendency for an increase of k 20 and reductions of a 30 , a 45 , and a 60 , then the traditional MCP were not much affected (Table 1). However, larger differences concerning the traditional MCP have been observed in dairy cows (Bittante et al, 2015).…”

Milk skimming, heating, acidification, lysozyme, and rennet affect the pattern, repeatability, and predictability of milk coagulation properties and of curd-firming model parameters: A case study of Grana Padano

“…In a large survey on Brown Swiss cows, Bittante et al (2015) prolonged the test duration to 90 min and observed in almost all samples a decrease in CF in the final part of the test due to syneresis and whey expulsion. In the present study, with a test duration of 60 min, the decreasing phase was not evident in the majority of samples nor could the syneresis instant rate constant be estimated.…”

Milk protein fractions strongly affect the patterns of coagulation, curd firming, and syneresis

“…A 10-mL aliquot of the 2-L subsample was used for determination of MCP by Formagraph (Foss Electric A/S) according to the method described in detail by Bittante et al (2015). Only rennet (0.051 IMCU/mL of milk) was added to each sample, and curd firmness was recorded every 15 s for 60 min by the instrument, yielding 240 measurements per milk sample, 4 of which were used to determine the traditional single-point MCP parameters [RCT, k 20 , a 30 , and curd firmness 45 min after rennet addition (a 45 )].…”

“…The model can also predict the maximum curd firmness estimated by the CF t function (CF max ) and the time taken to reach this value (t max ). To improve repeatability, CF P was estimated using a linear regression based on the CF max (CF P = 1.34 × CF max ) according to data recorded by Bittante et al (2015).…”