A large population study to assess the magnitude of prenatal programming in dairy cattle.

The performance of an adult dairy cow may be influenced by events that occur before her birth. The present study investigated the potential effects of 2 prenatal groups of factors, assisted reproductive technologies and maternal characteristics (e.g., dam parity), on offspring performance during their first lactation in populations of 2 dairy cow breeds: French Holstein and Montbéliarde. The different assisted reproductive technologies studied included the type of semen (conventional or X-sorted) used for AI and the technology of conception used (AI, embryo transfer, or in vitro fertilization). Three maternal characteristics were considered: (1) the dam age at first calving, (2) dam parity number, and (3) indicators of dam udder health during gestation (SCS and events of clinical mastitis). First, we investigated whether heifer survival from 3 d to 18 mo old was associated with any of the prenatal factors considered. We then estimated the associations of these prenatal factors with 8 traits of commercial interest: (1) stature, (2-4) milk, fat, and protein yields, (5) SCS, (6) clinical mastitis, and (7-8) heifer and cow conception rate, all measured on genotyped cows. Linear models were used for this study with the prenatal factors as covariates in the model, and for the 8 traits, phenotypes were adjusted for their corresponding genomic EBV. The results indicated that the survival rate of heifers born from embryo transfer was significantly higher than that of heifers born from AI (probably due to preferential management practices), and the other prenatal factors did not explain large differences in heifer survival. Among the Montbéliarde cows born from AI, those born from X-sorted semen showed a lightly but significantly lower milk yield than those born without X-sorting of the semen (-52 kg of milk in the first lactation). Among the Holstein cows, those born from embryo transfer presented significantly lower milk performance than cows born from AI. Regarding the maternal characteristics, none or very weak associations were found between the dam age at first calving and the offspring performance in both breeds. Dam parity, on the other hand, was associated with offspring performance for milk, fat, and protein yield in both breeds, but not in the same direction. In the Holstein breed, an increase in dam parity was favorable for offspring performance for milk, fat, and protein yield, whereas in the Montbéliarde breed, an increase in dam parity was associated with lower milk and protein yield and no association was found for fat yield. The udder health of the dam during gestation was not or only weakly associated with the traits studied in the offspring. Although some significant associations were identified due to the large sample size, the effects were modest, typically less than 1% of the phenotypic mean, and were not consistently observed across the 2 breeds.

Deciphering the segregation of proteins in high-protein dairy powders after spray-drying.

High-protein dairy powders are ingredients mainly produced by spray-drying, then subjected to aging during transport and storage. They often undergo physicochemical changes at this stage, such as the development of the Maillard reaction, primarily because of their intrinsic chemical properties, but also as a result of nonoptimal storage conditions. Components present at the particle surface are the first to be targeted by moisture and other environmental disruptions. Consequently, the identification, control, and prediction of particle surface components are useful to anticipate the effect of powder aging on product quality. Here, a new diafiltration method is proposed which fractionates proteins from a binary colloidal dispersion of 80% casein micelles and 20% whey proteins, according to their presence at the surface or core of the particle. This method shows that whey proteins are strongly enriched at the particle surface, whereas casein micelles are located at the core of the particles. This protocol also allows the identification of the rehydration kinetics for each rehydrated protein layer of the particle, revealing that 2 distinct forms of swelling occur: (1) a rapid swelling and elution of whey proteins present at the particle surface, and (2) a swelling of casein micelles located below the whey proteins, associated with a slow elution of casein micelles from the particles being rehydrated.

Structural markers of the evolution of whey protein isolate powder during aging and effects on foaming properties.

The market for dairy powders, including high added-value products (e.g., infant formulas, protein isolates) has increased continuously over the past decade. However, the processing and storage of whey protein isolate (WPI) powders can result in changes in their structural and functional properties. It is therefore of great importance to understand the mechanisms and to identify the structural markers involved in the aging of WPI powders to control their end use properties. This study was performed to determine the effects of different storage conditions on protein lactosylations, protein denaturation in WPI, and in parallel on their foaming and interfacial properties. Six storage conditions involving different temperatures (θ) and water activities (aw) were studied for periods of up to 12mo. The results showed that for θ≤20°C, foaming properties of powders did not significantly differ from nonaged whey protein isolates (reference), regardless of the aw. On the other hand, powders presented significant levels of denaturation/aggregation and protein modification involving first protein lactosylation and then degradation of Maillard reaction products, resulting in a higher browning index compared with the reference, starting from the early stage of storage at 60°C. These changes resulted in a higher foam density and a slightly better foam stability (whisking) at 6mo. At 40°C, powders showed transitional evolution. The findings of this study will make it possible to define maximum storage durations and to recommend optimal storage conditions in accordance with WPI powder end-use properties.