The Influence of Transition Diet Energy and Protein Content on Colostrum and Early Lactation Milk Composition and Bioactive Compound Concentrations in Holstein Dairy Cattle

Introduction

Bovine colostrum is largely known for its crucial role in providing the newborn dairy calf with immunoglobulin G (IgG) to establish passive immunity. However, IgG is only one of numerous colostral bioactive compounds – including hormones, fatty acids, and sialylated oligosaccharides (OS) – that have an unrealized potential to positively stimulate calf development (Fischer-Tlustos et al., 2021). In contrast to IgG, many of these bioactive factors remain elevated in transition milk (TM; milkings 2-6; Fischer-Tlustos et al., 2021) and may be responsible for observed benefits on calf intestinal development (Pyo et al., 2020), growth (Van Soest et al., 2020), and health (Conneeley et al., 2014) when TM is fed after the initial colostrum meals. However, concentrations of bioactive compounds in colostrum and TM vary greatly (Cabral et al., 2016; Fischer-Tlustos et al., 2020) and prepartum strategies to maximize their concentrations remain to be elucidated.

It is well known that altering prepartum dietary energy density influences prepartum dry matter intake (DMI), metabolism and energy balance (Janovick and Drackley, 2010; Mann et al., 2015; Haisan et al., 2021). It is hypothesized that these prepartum alterations in dam metabolism may influence the process of colostrogenesis in primiparous (PP) and multiparous (MP) cows; however, research regarding this concept is scarce. In addition, it is important to evaluate how prepartum energy density may interact with differing fresh cow diets, such as altered crude protein (CP) content, to influence TM composition. During the fresh period, cows experience a negative energy and protein balance (Bell et al., 2000) and protein derived from both the diet and body reserves is crucial in supplying amino acids and glucose to the mammary gland for milk synthesis (Bell et al., 2000). Thus, it is hypothesized that prepartum dietary energy density and postpartum CP content may interact to alter dam metabolism, which may affect TM composition and yield. Therefore, the objective of this study was to evaluate how prepartum dietary energy density affects colostrum composition and how pre- and postpartum dietary energy and CP content, respectively, affect TM and mature milk composition.

Materials and Methods

The animal experiment was a 2 × 2 factorial, randomized complete block design that involved MP (average parity = 2.4 ± 0.50, n = 28) and PP (n = 20) Holstein cows housed at Trouw Nutrition AgResearch Dairy Facility (Burford, ON, Canada). From -57 ± 5.8 d prior to expected calving, MP cows were dried off, and both MP and PP cows began a low energy diet (LED; 1.10 Mcal NEL/kg DM; 94% NEL requirements). From d -19 ± 4.0, animals were randomly assigned within block to a close-up diet (CUD) to either remain on the LED or to a high energy diet (HED; 1.52 Mcal NEL/kg DM; 129% NEL requirements). During the dry period, animals were housed in group pens and provided with treatment diets in an individual automated feed bunk (Calan Broadbent Feeding System). After calving, cows were moved to individual tie stalls and assigned to a postpartum diet (PPD) containing high protein (HPD; 18.5% CP, 1.73 Mcal NEL/kg DM) or average protein (APD; 15.5% CP, 1.68 Mcal NEL/kg DM) content. Cows were offered all diets once daily at 0900 h and refusals were collected and weighed daily to calculate DMI. A 100 mL colostrum sample was collected as soon as possible after calving, after which cows were milked twice daily at 0500 and 1600 h, and 50 mL samples of TM (milkings 2 to 7) and mature milk (16 ± 1.9 d postpartum) were collected. In all samples, fat, CP, lactose, milk urea nitrogen (MUN) and total solids (TS) concentrations were determined by mid infrared spectroscopy, IgG was quantified by radial immunodiffusion, and sialylated OS (3’sialyllactose (3’SL), 6’sialyllactose, 6’sialyllactosamine, and disialyllactose) were semi-quantified by LC-MS/MS using HILIC chromatography. Statistical analysis was conducted using SAS Studio (version 9.4, SAS Institute Inc., Cary, NC), with cow considered the experimental unit and as a random effect. Using PROC GLIMMIX, two separate models were used to determine 1) the effect of CUD on colostrum yield and composition, with the fixed effects of CUD, parity and their interactions and the random effect of block and CUD × block; and 2) the effect of CUD and PPD on TM and milk yield and composition, with the fixed effects of CUD, PPD, parity and their interactions, random effect of block, and repeated effect of milking. All values reported are least squares means and significance was declared at P < 0.05 and tendencies at 0.05 ≤ P < 0.10.

Results

There was no effect of CUD on colostrum yield (P = 0.625), colostrum IgG concentrations (P = 0.673) or other milk components (P > 0.251). However, colostrum SCC increased (P = 0.036) by 68.9% while colostrum 3’SL (P = 0.091) and total sialylated OS (P = 0.065) concentrations tended to decrease by 14.8% and 16.5%, respectively, in HED cows compared to LED cows. Aside from colostrum yield and composition, the HED also decreased the average concentrations of 3’SL (22.9%; P = 0.0079) and total sialylated OS (22.8%; P = 0.0027) concentrations compared to the LED over the entire sampling period. In regard to additional TM and milk components, it was clear that the prepartum diet had a greater influence on MP cows than PP cows; specifically, HEDMP cows had greater DMI at each week during the close-up period (P < 0.001) and during the 4 week fresh period (P = 0.049) compared to LED-MP cows, while HED-PP and LED-PP cows did not differ (P > 0.912) in DMI at any specific timepoints. These differences in pre- and postpartum DMI in MP cows may explain the observed increases in energy-corrected milk yield (29.4%; P = 0.008), fat yield (37.7%; P = 0.007), protein yield (14.0%; P = 0.036), total solids yield (35.3%; P = 0.020), and lactose yield (27.7%; P = 0.009) over the entire sampling period in HED-MP cows compared to LED-MP cows.

No differences (P > 0.999) were observed on colostrum, TM, and mature milk yield and composition within CUD between PP cows. The PPD did not affect postpartum DMI (P = 0.996), TM and mature milk yield (P = 0.182) and OS concentrations (P > 0.728). In contrast, cows fed the HPD had a 200, 86, and 15 g decrease in TS yield (P =0.062), protein yield (P = 0.040) and IgG yield (P = 0.046), respectively, compared to cows fed the APD diet over the sampling period. The HPD cows also had 3.4 mg/dL greater (P = 0.042) average MUN than HPD cows during the postpartum period. In contrast to the CUD, no differences were observed within parity between the PPD. The results revealed that there was largely no effect of CUD × PPD on TM and milk yield and composition (P > 0.271). Yet, HED-HPD and LED-HPD cows had 59.1 and 43.2% higher (P < 0.014) MUN, respectively, than HED-APD cows. Interestingly, LED-APD cows produced an additional 31.2 g (P = 0.025) of IgG compared to LED-HPD cows over the sampling period.

Implications and Conclusions

In contrast to previous studies (Mann et al., 2016; Fischer-Tlustos et al., 2021), altering prepartum dietary energy density did not influence colostrum IgG concentrations. These inconsistencies between studies may be explained by differences in energy level, as well as additional factors, such as management and production level. Interestingly, colostrum SCC increased in response to a high energy CUD; however, it is clear that prepartum udder health in HED cows was not compromised to such an extent that colostrum composition was negatively affected. Furthermore, colostrum OS concentrations decreased in HED cows, suggesting that further investigation regarding how dietary energy density may influence OS synthesis at the mammary gland level is required. Aside from colostrum, the results suggest that increases in pre- and postpartum DMI in response to increasing prepartum dietary energy density, as observed only in MP cows in the present study, may be a crucial factor responsible for the alteration of early lactation milk production and component yields.

Increasing CP content postpartum had negative effects on TS, protein, and IgG yield during the sampling period, and the observed higher MUN concentrations indicated inefficient protein utilization. The phenomena by which increasing postpartum CP content decreased IgG yield over the sampling period, especially in LED cows, requires further investigation given the low concentrations and yields of IgG in TM and mature milk compared to colostrum. In conclusion, these results suggest that increasing prepartum dietary energy density in MP cows may be a feasible strategy to increase TM component yields to improve young calf development and health.

Acknowledgements

The authors would like to thank the staff of the Trouw Nutrition AgResearch Dairy Facility (Burford, ON) for their assistance in animal feeding and sampling. This project was financially supported by Trouw Nutrition Canada and a Natural Sciences and Engineering Research Council of Canada (NSERC, Ottawa, ON) Alliance Grant in collaboration with the Saskatoon Colostrum Company Ltd. (Saskatoon, SK), Elanco Animal Health (Greenfield, IN, USA), and Land O’ Lakes Animal Milk Solutions Inc. (Arden Hills, MI, USA).

Presented at the 2022 Animal Nutrition Conference of Canada. For information on the next edition, click here.