Effects of various fat delivery methods in starter diet on growth performance, nutrients digestibility and blood metabolites of Holstein dairy calves

Effects of low-quality forage and starter protein content in starter diet of young calves on growth performance, rumen fermentation, and urinary purine derivatives

Feeding low-quality forage (LQF) has been evaluated in mature ruminants and results show that it has been improved nitrogen utilization efficiency. The present study evaluated the interaction effect of feeding wheat straw as LQF (0 and 7.5%, DM basis) and starter protein level (20 vs. 24%, DM basis) on growth performance, ruminal fermentation, and microbial protein synthesis in Holstein dairy calves raised under moderate heat stress condition. Forty-eight 3-day old dairy calves (averaging 40.6 kg) were assigned in four experimental treatments as follow; 1) no LQF with 20% CP (NLQF-20CP), 2) no LQF with 24% CP (NLQF-24CP), 3) 7.5% LQF with 20% CP (LQF-20CP) and 4) 7.5% LQF and 24% CP (LQF-24CP). The calves were weaned on d 53 of age but the experiment extended until d 73 of age. Feeding LQF increased starter intake, average daily gain (tendency), ruminal acetate concentration, and improved fecal score of calves. The average daily gains before and after weaning were positively influenced with greater starter protein content. Hence, weaning and final BWs were improved when calves received greater CP content. In addition, greater starter CP content increased total ruminal volatile fatty acid concentration. With respect to the interaction effect between LQF feeding and starter protein content, the lower nitrogen excretion through urine was obtained for LQF-20CP diet among experimental treatments. The results of the current study showed that feeding LQF improved ruminal fermentation pattern and improved growth performance through increased starter intake. In addition, greater starter protein content is advisable during pre-weaning period for calves raised under mild heat stress condition. In conclusion, based on the results found in the current study, it can be suggested that feeding LQF for calves under heat stress condition can improve nitrogen utilization when dietary protein content is low. This can be opportunity to formulate starter diets with greater nitrogen utilization efficiency which is critical for accelerated growth programs at early stages of growth for young calves while calves raised under hot season condition.

Starter protein content and supplemental soybean oil or hydrogenated palm fatty acids in Holstein dairy calves: growth performance, protozoa population, and nitrogen utilization efficiency

The study hypothesized that a 24% protein starter diet supplemented with inert fat (palm fatty acids; PLFs) instead of triglyceride-rich soybean oil (SBO) would promote the growth of dairy calves. The effects of different protein contents (20 vs 24% CP) and fat sources (SBO vs PLF at 2.5% DM) on growth, digestibility, blood metabolites, rumen protozoa and urinary nitrogen in dairy calves were investigated. A total of 52 female dairy calves (mean age 3 days and BW 40.7 kg) were allocated to the following treatments in a completely randomized design: (1) 20% CP starter diet supplemented with SBO (20CP-SBO), (2) 20% CP starter diet supplemented with PLF (20CP-PLF), (3) 24% CP starter diet supplemented with SBO (24CP-SBO), and (4) 24% CP starter diet supplemented with PLF (24CP-PLF). Calves were weaned on day 53, and the study ended on day 73. The 24CP diets enhanced starter feed intake, average daily gain (ADG), withers height, hip width, organic matter (OM) digestibility, and preweaning blood glucose compared to the 20CP diets. In contrast, SBO supplementation reduced feed intake, ADG, withers height, OM and CP digestibility, and pre- and postweaning blood glucose and beta-hydroxybutyrate levels, while increasing preweaning aspartate aminotransferase, compared to PLF. SBO supplementation led to lower urinary excretion of purine derivatives and microbial protein synthesis postweaning, and a reduction in protozoa population both pre- and postweaning. Calves fed PLF had higher starter intake than those fed SBO, regardless of the diet being 20CP or 24CP. Calves fed the 24CP-PLF diet had the highest ADG, while calves fed the 20CP-SBO diet had the lowest ADG. Calves fed the 20CP-SBO diet had lower feed efficiency than calves fed the other diets during the preweaning period and throughout the experimental period. Calves fed the 24CP-PLF diet had higher hip heights at weaning and on day 73 than calves fed the other diets. Calves fed the 20CP-SBO diet had lower neutral detergent fiber digestibility than calves fed the other diets. Calves fed the 24CP-SBO diet had higher postweaning blood urea nitrogen concentration than calves fed the other diets. Feeding the 20CP-SBO diet to dairy calves decreased urinary allantoin excretion and rumen microbial protein synthesis but increased urinary nitrogen excretion during the preweaning period. Our results suggest that PLF is more suitable than SBO in calf diets, especially when calves fed 24% CP, possibly due to improved nutrient digestibility.

Effects of fat source in calf starter on growth performance, blood fatty acid profiles, and inflammatory markers during cold season

This study was conducted to investigate the effects of supplementation of different fat sources in calf starters on growth performance, health, blood fatty acid profiles, and inflammatory markers during the cold season in dairy calves. A total of 48 Holstein calves (24 males and 24 females) were randomly assigned to 1 of 4 starter diets throughout the experiment (d 3 to 65): (1) no supplemented fat (CON), (2) 3% calcium-salts of soybean oil (Ca-SBO), (3) 3% calcium-salts of fish oil (Ca-FO), and (4) 3% mixture of Ca-SBO and Ca-FO (1.5% each, DM basis; MIX). Calves were given free access to starter feed and water and were raised individually in pens from 3 to 65 d of age. Calves fed Ca-SBO consumed a greater proportion of n-6 FA, while calves fed Ca-FO consumed a greater level of n-3 FA compared to the other dietary treatments. Fat supplementation increased the intake of linoleic acid, the major n-6 FA, with the greater intake observed in the Ca-SBO group compared to the other dietary treatments. Calves fed the Ca-FO and MIX diets consumed more long-chain n-3 FA than the other diets. In addition, calves fed Ca-SBO and Ca-FO diets consumed more starter feed and total dry matter than calves fed MIX and CON throughout the experiment (d 3 to 65). Calves fed Ca-FO had higher average daily gain throughout the trial (d 3 to 65) than the other treatment groups. Of all treatment groups, calves fed Ca-FO achieved the highest final body weight and showed the greatest feed efficiency. Random forest analysis revealed that eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and arachidonic acid were the serum levels of FA most affected by the diets. The principal component analysis of blood FA profile, blood parameters, and inflammatory markers showed distinct differences between dietary treatments. Calves fed Ca-SBO had higher plasma concentrations of linoleic acid, while calves fed Ca-FO had higher plasma concentrations of long-chain n-3 polyunsaturated fatty acids (PUFA), such as EPA, docosapentaenoic acid (DPA), and DHA than the other treatment groups. Plasma inflammatory markers were lower in calves fed Ca-FO and higher in calves fed CON than in the other treatment groups. The Ca-FO group had lower levels of inflammatory markers, including serum amyloid A, tumor necrosis factor-alpha, Interferon-γ, haptoglobin, and interleukin-6 compared to the other experimental treatments. Also, the blood malondialdehyde levels, an indicator of oxidative stress, were lower in calves fed Ca-FO compared with calves fed the other treatment diets. In conclusion, the performance of preweaned dairy calves can be improved by adding fat to their starter feed under cold conditions. Overall, the type of fat in milk may affect growth and inflammation of dairy calves before weaning under cold conditions, with n-3 FA (Ca-FO) promoting growth and reducing inflammation more effectively than n-6 FA (Ca-SBO).

The type of lipid supplement has crucial implications for forage particle size in calf starter diets

BACKGROUND

Forage inclusion in starters of young dairy calves has become an acceptable strategy in the last decade. To compensate for the lower energy provided by forage, concurrent lipid supplementation can be proposed. However, ruminal microbial activity and forage digestibility may be decreased by lipid supplementation. We hypothesized that the composite effect of forage and lipid supplements may be dependent on forage particle size and the type of lipid supplement. Therefore, we evaluated the effect of long (LP; geometric mean, 4.97 mm) vs. short alfalfa hay particle sizes (SP; geometric mean, 1.26 mm) with either soybean oil (SBO) or palm fatty acids (PLF) as lipid source in a 2 × 2 factorial design with treatments SP-SBO, SP-PLF, LP-SBO, and LP-PLF. Treatments (n = 13 with 6 males and 7 females each) were offered to Holstein calves (3 days old) with equal amounts of lipid (25 g/kg DM) throughout the experimental period. The milk offering scheme (d 1 to 53) was equal for all groups. Data collection continued until 20 d post-weaning.

RESULTS

Interaction between forage particle size and lipid supplement was significant for the following readouts: the highest and lowest starter intakes during the pre-weaning period occurred in LP-PLF and LP-SBO, respectively. This was associated with similarly contrasting changes in average daily gain (ADG) during the post-weaning period, body weight at the end of experiment, withers height, digestibility of organic matter and neutral detergent fiber, and blood serum concentrations of glucose, beta-hydroxybutyrate, and insulin during the pre-weaning period. During both pre- and post-weaning periods, the highest and lowest urinary excretion of allantoin and total purine derivatives, representing microbial protein synthesis, were observed in LP-PLF and LP-SBO, respectively, indicating that those diets were most and least favorable for rumen development. Irrespective of forage particle size, supplemental SBO vs. PLF increased serum malondialdehyde as an oxidative stress indicator across periods, increased blood urea nitrogen and feed efficiency in the pre-weaning period, and reduced hip height during the post-weaning period.

CONCLUSIONS

It can be concluded that feeding a rumen-inert, mostly saturated fatty acid source with alfalfa hay as long particle size is recommended with view on performance, whereas a combination soybean oil rich in unsaturated fatty acids should not be provided to milk-fed Holstein calves together with long particle forage. Feeding soybean oil and alfalfa hay as long particles is not advisable mainly due to lower starter consumption and impaired development of ruminal function. If dietary supplementation of soybean oil is applied, incorporation of forage as small particles should be preferred to support rumen development.

Impact of corn processing and weaning age on calf performance, blood metabolites, rumen fermentation, and behavior

This study examined the impact of two corn processing methods (steam-flaked (SFC) vs. ground) combined with two weaning ages (50 or 75 days) on calf performance, blood metabolites, rumen fermentation, nutrient digestion, and behavior. The study involved 48 three-day-old Holstein calves, with an average body weight of 41.4 ± 2.2 kg. The experimental design was a 2 × 2 factorial arrangement, resulting in four treatment groups: SFC50 (SFC and weaning at 50 days), SFC75 (SFC and weaning at 75 days), GC50 (ground corn and weaning at 50 days), and GC75 (ground corn and weaning at 75 days). Calves were given whole milk at 4 L/ day from day 3-15 and 7 L/ day from day 16 to either 43 or 68, depending on weaning age. Weaning occurred between days 44 and 50 for early-weaned calves and between days 69 and 75 for late-weaned calves. The study lasted until calves were 93 days old. The starter ration consisted of soybean meal, corn grain, 5% chopped wheat straw and premix. Results indicated that the SFC-based starter feed improved calf performance and nutrient digestion, as evidenced by increased weight gain, dry matter, crude protein, and neutral detergent fiber digestibility. Calves fed the SFC-based starter diet had lower blood albumin and urea N concentrations, while blood total protein and globulin concentrations were higher, especially in early-weaned calves. No significant changes in rumen pH and ammonia-N concentration were observed. In addition, the SFC starter feed resulted in higher volatile fatty acids concentration and longer feeding time in weaned calves compared to ground corn. Overall, these results suggest that an SFC-based starter feed may be beneficial for both early and late weaned calves.

Effects of Soybean and Linseed Oils Calcium Salts and Starter Protein Content on Growth Performance, Immune Response, and Nitrogen Utilization Efficiency in Holstein Dairy Calves

This study aimed to investigate the interaction of fatty acid (FA) source [calcium salt of soybean oil (n-6 FA) vs. calcium salt of linseed oil (n-3 FA) both 3% DM basis] with protein content (18% vs. 22% CP, based on DM) on growth performance, blood metabolites, immune function, skeletal growth indices, urinary purine derivatives (PD), and microbial protein synthesis (MPS) in young dairy calves. Forty 3-day-old calves (20 females and 20 males) with a starting body weight (BW) of 40.2 kg were assigned in a completely randomized block design in a 2 × 2 factorial arrangement of treatments. Experimental diets were: (1) n-6 FA with 18% CP (n-6-18CP), (2) n-6 FA with 22% CP (n-6-22CP), (3) n-3 FA with 18% CP (n-3-18CP), and (4) n-3 FA with 22% CP (n-3-22CP). Starter feed intake and average daily gain (ADG) were not influenced by experimental diets (p > 0.05). However, before weaning and the entire period, feed efficiency (FE) was greater in calves fed n-3 FA compared to n-6 FA (p < 0.05). Heart girth (weaning, p < 0.05) and hip height (weaning, p < 0.05 and final, p < 0.01) were highest among experimental treatments in calves who received n-3-22CP diets. The greatest blood glucose (p < 0.05) and insulin (p < 0.01) concentrations in the pre-weaning period and the lowest serum concentration of tumor necrosis factor (before weaning, p < 0.05) were observed in calves fed the n-3-22CP diet. However, the greatest blood urea N (before weaning, p < 0.05; after weaning, p < 0.05) and urinary N excretion (p < 0.05) were found in calves fed n-6-22CP diets compared to other experimental arrangements. In conclusion, offering calves with Ca-salt of n-3 FA along with 22% CP content may be related to improved nitrogen efficiency and immune function.

Effects of linseed oil supplementation in Holstein dairy calves received starters based on either corn or barley grain on growth performance and immune response

This study evaluated the effects of linseed oil (LO) and two-grain sources on growth performance, microbial protein yield (MPY), blood metabolites, and inflammatory markers in Holstein dairy calves. Forty-eight 3-day-old dairy calves (24 males and 24 females) with starting BW of 40.3 ± 1.6 kg were allocated in a completely randomised block design with a 2 × 2 factorial arrangement as follows; (1) Corn grain (CG) with no LO supplementation (CG-NLO), (2) CG with 2.5% LO supplementation (CG-LO), (3) Barley grain (BG) with no LO supplementation (BG-NLO), and (4) BG with 2.5% LO supplementation (BG-LO). The calves were weaned on d 59 but the study lasted for 14 days after weaning (Day 73 of experiment). The results showed that starter feed intake was influenced neither by grain source nor linseed oil. However, average daily gain, BW, hip height, and MPY were improved in calves received BG compared to CG diets. Linseed oil supplementation had no significant effects on growth performance and MPY. During preweaning period, calves fed BG-LO had the greatest feed efficiency and the highest wither height. However, the greatest tumour necrosis factor and serum amyloid A were observed in BG-NLO. Despite, LO supplementation did not influence growth performance of animals per se; however, it reduced circulating inflammatory markers in calves during preweaning period. Based on this study condition, BG is more favourable than CG in dairy calves from the daily gain and microbial protein synthesis perspectives, and supplementing the starters with n-3 FA can be strategy to improve immune performance of calves fed barley-based starter diets.

Alfalfa Xeno-miR168b Target CPT1A to Regulate Milk Fat Synthesis in Bovine Mammary Epithelial Cells

It was shown that microRNAs (miRNAs) play an important role in the synthesis of milk fat; thus, this manuscript evaluated whether exogenous miRNA (xeno-miRNAs) from alfalfa could influence the milk fat content in dairy cows. At first, mtr-miR168b was screened from dairy cow milk and blood. Then, EdU staining, flow cytometry, Oil Red O staining, qRT-PCR, and WB were applied to explore the effect of xeno-miR168b on the proliferation, apoptosis, and lipid metabolism of bovine mammary epithelial cells (BMECs). Finally, in order to clarify the pathway that regulated the lipid metabolism of BMECs using xeno-miR168b, a double-luciferase reporter assay was used to verify the target gene related to milk fat. These results showed that overexpression of xeno-miR168b inhibited cell proliferation but promoted apoptosis, which also decreased the expression of several lipid metabolism genes, including PPARγ, SCD1, C/EBPβ, and SREBP1, significantly inhibited lipid droplet formation, and reduced triglyceride content in BMECs. Furthermore, the targeting relationship between CPT1A and xeno-miR168b was determined and it was confirmed that CPT1A silencing reduced the expression of lipid metabolism genes and inhibited fat accumulation in BMECs. These findings identified xeno-miR168b from alfalfa as a cross-kingdom regulatory element that could influence milk fat content in dairy cows by modulating CPT1A expression.

Supplementation of n-3 fatty acid and ruminal undegradable to degradable protein ratio in young lambs raised under heat condition: effects on growth performance and urinary purine derivatives

The present study evaluated the effect of supplementation alpha-linolenic fatty acid source (ALA) with different rumen undegradable to degradable protein ratios [low ratio (LR) = 26:74; high ratio (HR) = 36:64 based on CP%] on growth performance, nutrient digestibility, fecal score, animal feeding behavior, and urinary purine derivatives (PD) in young lambs during hot season. Forty 10-day-old lambs (averaging body weight of 7.9 ± 0.8 kg) were used in a completely randomized block design with a 2 × 2 factorial arrangement as following treatments (10 lambs/treatment): (1) no n-3 FA supplementation with LR diet (NALA-LR), (2) no ALA supplementation with HR diet (NALA-HR), (3) supplementation of ALA with LR diet (ALA-LR), and (4) supplementation of ALA with HR diet (ALA-HR). Results showed that ALA supplementation slightly increased feed efficiency (FE; tendency, P = 0.076), improved fecal score (P = 0.045), and reduced rectal temperature (tendency, P = 0.064) during pre-weaning period. The HR diets improved average daily gain (ADG; P < 0.01), wither height (post-weaning; P = 0.015), and final BW (P = 0.048) compared with LR diets. The greatest ADG (pre-weaning; P = 0.012), structural growth, and the lowest urinary nitrogen exertion (P = 0.043) were found in the ALA-HR treatment. No change was found for ruminal fermentation, nutrient digestibility, and animal behavior in lambs fed different experimental treatments. In summary, results indicated that concurrent feeding of ALA and high dietary RUP:RDP ratio can be recommendable that is likely due to more efficient nitrogen utilization when young lambs are raised during hot season. HIGHLIGHTS: • The interaction of n-3 FA and nitrogen was evaluated in pre-weaning lambs raised under heat condition. • Supplementation of n-3 FA increased FE and improved fecal score in heat-exposed lambs during pre-weaning period. • The high RUP:RDP ratio improved skeletal growth during post-weaning period. • Concurrent feeding of n-3 FA and high dietary RUP:RDP ratio is recommendable in young lambs raised during hot season.

Effects of protein content and rumen-undegradable to rumen-degradable protein ratio in finely ground calf starters on growth performance, ruminal and blood parameters, and urinary purine derivatives

This study investigated the effects of feeding finely ground starter diets containing either 18 or 22% crude protein (CP) content [dry matter (DM) basis] and high or low ratios of rumen-undegradable protein to rumen-degradable protein (RUP:RDP) on growth performance, nutrient digestibility, ruminal fermentation, blood metabolites, and urinary purine derivatives in dairy calves. A total of 48 three-day-old female Holstein dairy calves with 40.2 ± 2.5 kg of initial body weight (BW) were randomly assigned in a complete randomized block design to a 2 × 2 factorial arrangement of treatments (12 calves/treatment). Treatments were as follows: (1) finely ground starter diet (mean particle size = 0.69 mm) with 18% CP and low RUP:RDP ratio [low ratio (LR) = 26:74; 18CP-LR]; (2) finely ground starter diet with 18% CP and high RUP:RDP ratio [high ratio (HR) = 35:65; 18CP-HR]; (3) finely ground starter diet with 22% CP and low RUP:RDP ratio (22CP-LR); (4) finely ground starter diet with 22% CP and high RUP:RDP ratio (22CP-HR) on DM bases. Blocking was based on the day of treatment assignment, and treatments were randomly assigned within each block. Calves received 4 L of milk daily from d 3 to 10, 7 L/d from d 11 to 40, 4 L/d from d 41 to 49, and 2.5 L/d from d 50 to 53, and then all calves were weaned but remained in the experiment until d 83 of age. The results showed that overall average daily gain (ADG), weaning BW, and feed efficiency (FE) were greater in 22% CP treatments than in 18% CP. Increasing the starter CP content from 18 to 22% of DM did not influence overall starter feed intake, milk intake, total dry matter intake (DMI), postweaning ADG, and FE of calves. No effect of RUP:RDP ratio was observed for starter feed intake, milk intake, total DMI, preweaning ADG, FE, and grams of CP per megacalorie of metabolizable energy. The RUP intake and postweaning ADG were greater for calves fed the HR diets than for those fed the LR diets. The digestibility of neutral detergent fiber was greater, and the digestibility of OM tended to be greater, and the ruminal concentrations of total short-chain fatty acids (SCFA), acetate proportion, and acetate-to-propionate ratio were greater in 22% CP than in 18% CP. A 2-way interaction between starter protein content and time was observed for total ruminal SCFA, acetate proportion, and acetate-to-propionate ratio, indicating that starter CP concentration had more effect on ruminal parameters. Preweaning urinary purine derivatives, preweaning microbial protein synthesis, and postweaning urinary nitrogen were greater for calves fed the 22CP diets than for those fed the 18CP diets but were not affected by the different RUP:RDP ratios. The concentrations of blood glucose and insulin were greater in 22% CP than in 18% CP diets. The blood insulin concentration was greater when calves received the HR diets compared with the LR diets. Therefore, we conclude that greater starter protein content can have beneficial effects on growth performance, probably through increased microbial protein synthesized and preweaning blood insulin concentration; however, a greater RUP:RDP ratio showed marginal effects on growth performance during the postweaning period.

The effect of supplemental bioactive fatty acids on growth performance and immune function of milk-fed Holstein dairy calves during heat stress

The present study aimed to evaluate the effects of different supplemental fat sources (soyabean oil (SBO) as a source of n-6 fatty acid (FA) and fish oil (FO) as a source of n-3 FA) in the starter feed of milk-fed dairy calves during the hot season. Forty Holstein calves (3 d of age; 39·67 kg of body weight; ten calves per group) were randomly assigned to the experimental treatments as follows: (1) starter feed supplemented with no fat source (CON), (2) starter feed supplemented with 3 % SBO (DM basis), (3) starter feed supplemented with 3 % FO (DM basis) and (4) starter feed supplemented with an equal mixture of SBO and FO (1·5 % each, DM basis). The milk feeding schedule was constant for treatments and all calves were weaned on day 65 of age. Results show that calves had greater starter intake, average daily gain and body length when fed SBO compared with the other treatments. However, feed efficiency was increased and inflammatory indicators (TNF-α, serum amyloid A and haptoglobin) concentrations were reduced in the calves fed FO compared with the other treatments. In summary, it was revealed that SBO rich in n-6 FA improved starter intake and growth performance, while FO rich in n-3 FA could improve the immune function of calves. Due to the current experimental condition, an equal mixture of SBO and FO (1·5 % each, DM basis) can be recommended to have an optimum growth performance and immune function while the calves are reared under the heat conditions.

Effects of supplemental fat sources and forage feeding levels on growth performance, nutrient digestibility, ruminal fermentation, and nitrogen utilization in dairy calves

Knowledge regarding the potential interactions between supplemental fat source and fiber level in starter diet of dairy calves is lacking. The aim of the present study was to investigate the effects of supplemental saturated fat [palm fat (PLF) containing 86% palmitic acid (C16:0)] vs. unsaturated fat [soybean oil (SBO) containing 51% linoleic acid (C18:2)] and forage level on feed intake, growth performance, ruminal fermentation, nutrient digestibility, and metabolic traits in dairy calves. Forty newborn Holstein female calves (BW = 39.7 ± 1.8 kg) were assigned to 1 of 4 treatment groups (each consisting of 10 animals) in a 2 × 2 factorial arrangement of fat source [soybean oil vs. palm fat; 3% of starter based on DM basis] and alfalfa hay level (0 vs. 15%, on DM basis): SBO or PLF with (AH) or without (NAH) alfalfa hay. Calves had ad libitum access to water and starters throughout the study and a constant amount of milk was offered among experimental calves during the pre-weaning period. All calves were weaned on day 63 of age and remained in the study until day 73 of age. The results showed that the lowest and the highest starter intake and average daily gain during pre-weaning period was observed when calves received SBO-AH and PLF-AH, respectively. Accordingly, the lowest wither and hip heights at weaning time (day 63) and final wither height (day 73) were observed in SBO-AH group across treatments. Calves received PLF-AH had the highest weaning and final BW compared to other groups. Feed efficiency tended to be higher in PLF groups compared with SBO calves. Calves fed SBO-AH had the lowest digestibility of organic matter and neutral detergent fiber and also total short chain fatty acid concentrations in rumen compared with other groups. The SBO calves had lower urinary allantoin, urinary purine derivatives, and microbial protein synthesis than PLF calves; however, urinary nitrogen increased with SBO supplementation. In summary, the supplementation of SBO rich in C18:2 and AH during the pre-weaning period resulted in negative responses on growth performance, digestibility, and ruminal fermentation profile. Therefore, the inclusion SBO rich in C18:2 along with forage in the starter is not recommendable for young dairy calves.

Soybean oil supplementation and starter protein content: Effects on growth performance, digestibility, ruminal fermentation, and urinary purine derivatives of Holstein dairy calves

This study investigated the effects of feeding dairy calves starter diets containing 19% or 22% crude protein (CP) content on a dry matter basis and either supplemented or not with soybean oil (SBO, 0 vs. 3%, dry matter basis) on growth performance, digestibility, urinary nitrogen, and purine derivatives (PD) excretion. A total of 48 female Holstein dairy calves (mean 39.8 kg of body weight) were randomly distributed to experimental diets in a 2 × 2 factorial arrangement of treatments. The 4 dietary treatments were (1) starter diet without SBO supplement and 19% CP (NSBO-19CP), (2) starter diet without SBO supplement and 22% CP (NSBO-22CP), (3) starter diet with 3% SBO and 19% CP (SBO-19CP), and (4) starter diet with 3% SBO and 22% CP (SBO-22CP). Milk feeding value was similarly based on a constant protocol across experimental treatments and calves had ad libitum access to water and starter diets throughout the study. All calves were weaned on d 63 of age and remained in the study until d 83 of age. Calves supplemented with SBO had lower starter feed intake and average daily gain (ADG) and lower feed efficiency (FE) but had a higher fecal score indicating a higher likelihood of diarrhea occurrence compared with unsupplemented calves. Wither heights, digestibilities of organic matter, CP, and neutral detergent fiber were decreased, and ruminal volatile fatty acids tended to be reduced, and the molar proportion of ruminal butyrate (preweaning) and acetate (postweaning) reduced by supplemental SBO. The urinary allantoin and total PD excretion were reduced; however, urinary nitrogen excretion was increased when calves were supplemented with SBO. The CP amount did not affect starter feed intake, FE, or diarrhea occurrence rate, whereas the 22CP diets increased neutral detergent fiber digestibility, improved ADG (tendency), and increased allantoin and urinary PD excretion compared with the 19CP diets. The starter feed intake, ADG, FE, diarrhea occurrence rate, nutrient digestibility, and ruminal fermentation were not affected by the interaction between starter SBO and CP level; however, hip height and total PD in calves that received the SBO-22CP diets were higher than those fed the SBO-19CP diets. In conclusion, based on our experimental conditions, supplemental SBO could not be recommended for dairy calves. Furthermore, our findings indicate that SBO has negative effects on performance more attributed to reducing starter intake, digestibility, and ruminal volatile fatty acid concentration rather than because of a limitation of starter metabolizable protein supply and intestinal amino acid availability. Therefore, our results indicate that feeding the higher starter CP content is not a viable strategy to compensate for the negative effects of SBO supplementation on the growth performance of dairy calves.