Recent Advances in Calf Gut Health and Nutrition for Augmenting Growth

Recent Advances in Calf Gut Health and Nutrition for Augmenting Growth

Dr. Sheizal Minhas

Department of Animal Nutrition, College of Veterinary Sciences, GADVASU, Ludhiana, Punjab 141004, India

Sheizal.minhas18@gmail.com

Summary

Knowledge of calf nutrition is essential for a profitable dairy farming. Optimum nutrition of calves improves growth rate as well as decrease incidence of mortality due to scouring. The digestive tract of calves develops from a pre-ruminant to ruminant digestive system. The feeding of calves also transitions accordingly from liquid feed to solid feed intake. Colostrum, milk, milk replacer, calf starter, roughage and water should be provided to calves with the aim of improving immunity, reduce loss due to disease and mortality, enhance growth and production. The focus has increased recently on importance of bioactive compounds in dam’s colostrum and milk for gut health and development. Feed additives also play an important role in enhancing calf growth performance.

Introduction

Feeding of calf is important for:

1. Improving growth rate
2. Early rumen development
3. Reach puberty early
4. Improve lactation performance

The weaning to calf, in nature, takes about 8 to 10 months. In dairy farm practice, the weaning is done as early as 6-8 weeks. In India, calves are reared mainly for milk production. To reduce the cost of feeding the calves while still fulfilling their nutrient requirement is a challenge. The strategies like early weaning, feeding calf starters and milk replacers are employed to encourage calves to consume soild feed and spare dam’s milk for human consumption. This increases the profitability of the farmers.

Challenges of early weaning:

1. Low immunity of claves
2. Poor weight gain
3. Calf diarrhoea
4. Delayed conception in heifers
5. Mortality among calves

Indiscriminate use of antibiotics in calves with diarrhoea poses threat of antibiotic resistance of microbes.

Therefore, importance of calf gut health and nutrition is indispensable for a successful dairy farm.

Digestive Tract Development of Calf

1)  Pre-ruminant digestion/Liquid-feeding phase (3-4 weeks)

Abomasum constitutes nearly 70% of all stomach compartments. The rumen is smaller. Digestive system functions like that of a young monogastric animal. The calf depends on colostrum and milk or milk replacer. Sucking action causes closing of reticular/esophageal groove (a fold of muscle in the rumen wall) and milk directly passes to abomasum. Enzymes like rennin (milk protein digestion) and lactase (lactose digestion) are predominant in the first few weeks of age. Pepsin secretion increases after 3-4 weeks and helps in protein digestion. It is therefore, important to avoid giving non-milk protein in milk replacers during first three weeks of age. Calves are also unable to utilize starch at this stage.

2)   Transition phase (4-8 weeks)

Calf begins consuming solid feed. Consumption of solid feed does not stimulate the closure of the oesophageal groove and therefore, enters rumen for fermentation. Soild feed enhances rumen development. Rumen is populated with micro-organisms from environment and produce volatile fatty acids (VFA) upon fermentation of solid feed, which causes development of rumen papillae. The size and musculature of rumen also increases.

3)  Ruminant digestion

The ruminant phase begins at about six to eight weeks of age. Calves can be weaned at this stage. Only solid feed is consumed (no milk or milk replacer) as source of feed. Rumen accounts for 70% of all stomach compartments. It takes 12 to 16 weeks for rumen to become fully functional.

Colostrum

Colostrum is the secretion produced by the mammary gland immediately following parturition. Cow colostrum is a thick, yellow, and slightly acidic (pH 6.4) liquid.

Following are the functions of colostrum:

1. Protection- source of passive immunity
2. Nourishment- provides nutrition to young calf
3. Purgation- helps in voiding meconium (first feces of calf)

Bovine colostrum is a source of various nutrients (Fat, protein, carbohydrates, essential amino acids, vitamins & minerals) and non-nutritive bioactive compounds (Lactoferrin, lactoperoxidase, lysozyme, oligosaccharides, leukocytes, growth factors & immunoglobulins). Colostrum is richer in protein (casein and whey protein), fat, vitamins and minerals as compared to dam’s whole milk. The concentration of lactose in milk is higher as compared to colostrum.

The composition of colostrum changes with each milking. The protein and fat concentrations decrease while lactose concentration increases as it transitions towards whole milk secretion. Colostrum should be provided (10% of body weight) immediately after birth (0.5–1 hour). The ability to absorb the immunoglobulins from colostrum decreases by 33% within 6 hours and 66% after 12 hours of birth. A gut barrier is established after 24 hours.

MILK

Milk can be fed to calves as following;

First 3 weeks of age- 1/10^th of Body Weight

4-5 weeks of age- 1/15^th of Body Weight

Then onwards- 1/20^th of Body weight

Restricted milk feeding encourages solid feed consumption in calves. This helps in early rumen development. The solid feed can be supplemented in the form of highly digestible calf starter.

In many dairy farms, dam’s milk is entirely or partially substituted with milk replacer for providing liquid feed to calves.

Milk Replacer

Milk replacer is a dry feed mixture reconstituted with warm water to be given as a replace for milk. Milk replacer reduces risk of disease transmission through unpasteurized dam’s milk. It also helps to economize calves rearing.

Milk replacer should be fed atleast twice daily from second week till weaning. Milk replacer is composed of 20 to 24% crude protein (CP), 15-20% fat and low in fibre (less than 0.1%). Minerals, vitamins, and additives like antibiotics may be added. Emulsifier such as lecithin (2%) is added in milk replacer to help in reconstitution with water. The nutritional composition of milk replacer should be similar to dam’s whole milk.

Protein sources for milk replacer:

1. Milk protein such as casein protein or whey protein.
2. Plant based protein such as wheat gluten protein or soya protein (preferably to calf  >3 weeks of age). Plant based milk replacers require proper balancing of amino acids to ensure all essential amino acids are available to the calf. It should also be checked for presence of any anti-nutritional factors.

Fat sources for milk replacer:

1. Milk fat e.g. butterfat.
2.  Plant sources e.g. Vegetable oil (can cause diarrhoea due to high polyunsaturated fatty acid content).

Milk replacers lack bioactive compounds (found in colostrum as well as milk). Also, plant origin milk replacers may contain antinutritional factors. This may lead to delay in the development of gastrointestinal tract of calves.

Calf Starter

It is a highly digestible and palatable solid concentrate feed. It is provided from three weeks of age as milk intake is gradually decreased. It should contain 18% Digestible Crude Protein or 23-26% CP, 75% Total digestible nutrients (TDN), <7% Fiber and Fat upto 4%.

Ingredients such as crushed Barley, soya flakes, ground nut cake, maize, bran, dried skim milk, molasses etc can be added to constitute calf starter. One can start providing with as low as 100g per day per calf and gradually increase the amount. Calf should be able to consume atleast 1 kg of starter feed by the time of weaning.

Roughage

Calves are provided with roughage in the form of long dry hay or leguminous green fodder at about 8 weeks of age. Calves generally start to nibble on dry hay from as young as three weeks old. It helps in early development of forestomach of calves. The contractions in rumen promote development of muscle layer of the rumen. Overfeeding of fibrous roughage should be avoided as it will not digest properly and may lead to delay in rumen development.

Water

Water should always be available to calves from 3-4 days of age. Calves generally drink about five liters of water for every one kg of dry solid feed consumption (in addition to liquid feed intake).

Water consumed, especially after solid feed intake, directly goes into rumen. This helps in creating an optimal environment for rumen fermentation. It has been observed that calves fed water have more dry matter intake, less incidence of calf diarrhoea and better grow rate.

Bioactive components in colostrum/milk

Bioactive components are derived in colostrum/milk from either plasma of dam (immunoglobulin G, growth hormone (GH), prolactin (PRL), insulin, glucagon etc.) or secreted by lactocytes in mammary gland (Immunoglobulin A, Insulin like growth factors (IGF), Micro RNAs (miRNAs), lactoferrin, lactoperoxidase etc.).

These bioactive compounds play role in;

1, Providing passive immunity to calf (Immunoglobulins, Trypsin inhibitors, leukocytes).

2. Aids in colonization of beneficial gut microbes (Oligosaccharides, Anti-microbial peptides).
3. Gut epithelial development and barrier function (Hormones, growth factors etc.).

1) Immunoglobulins (Ig): Colostrum is rich in immunoglobulins. It provides passive immunity to young calf. Concentration of different Ig in colostrum: IgG1 (80-90% of Total IgG)>IgM>IgA>IgG2. A calf requires at least 150-200g of Ig within 2 hours after birth. It can be ensured by feeding 3-4 liters of colostrum with Ig >50mg/ml. Calf serum containing more than 10 mg IgG/ml after consuming colostrum, is considered as successful transfer of passive immunity.

2) Trypsin inhibitors protect Ig from proteolysis. It thus helps in absorption of intact Ig by calf intestinal mucosa.

3) Fatty acids: Colostrum has higher concentration of polyunsaturated omega-3 fatty acids as compared to milk (increase synthesis of Glutathione peroxidase and Superoxide dismutase, improving antioxidant capacity). On the other hand, Butyrate concentration in milk is nearly double that of colostrum. Butyrate in milk plays an important role in developing lower gut epithelium.

4) Maternal Leukocytes also provide passive immunity to the calf after ingestion of colostrum. They are also present in milk in considerable amount.

5) Oligosaccharides (OS): Colostrum and milk are considered best prebiotic for calves. More than 50 different OS have been discovered in colostrum. Sialylated OS are predominant OS in bovine colostrum. The OS are not digested by the host but nourish beneficial bacteria such as Bifidobacterium, Lactobacillus. OS mimics host cell surface receptors and thus inhibits adhesion of pathogens to intestinal mucosa. OS also improves intestinal barrier by stimulating production of mucus by intestinal epithelium.

6) microRNA: miRNAs are a group of small, non-coding RNA molecules that regulates gene expression at post-transcriptional level. miRNAs are transported in extracellular vesicles in colostrum/milk which protects it from acidic environment of abomasum. miRNAs are mainly involved in mucosal immune system development in the small intestine.

7)  Anti-microbial Peptides: such as Lysozyme, Lactoferrin, Lactoperoxidase and Proline-rich polypeptides prevent proliferation of harmful microbes. Lysozyme cleaves β1,4-linkages between muramic acid and N-acetylglucosamine in bacterial cell walls (It is therefore more effective against Gram-positive bacteria). Lactoferrin is responsible for intestinal absorption of iron. It also stimulates phagocytes and immunological responses. Lactoperoxidase produces reactive oxygen species (ROS) which suppress harmful bacterial growth in GIT. Proline-rich polypeptides disrupt acidic cell membrane of mostly gram-negative bacteria.

8) Growth Factors are present in colostrum and milk, such as:

Insulin-like growth factors (IGFs): Stimulate enterocyte proliferation (IGF-I) and differentiation (IGF-II), promoting gut development and regeneration.

Epidermal growth factor (EGF): Activates EGF receptor signaling, enhancing cell proliferation, angiogenesis, and reducing apoptosis in intestinal tissues.

Transforming growth factor (TGF-β): Regulates immune responses, controls inflammation, and supports intestinal cell proliferation.

Fibroblast growth factors (FGFs): Encourage epithelial repair and vascular development in the gastrointestinal tract.

Betacellulin (BTC) and Platelet-derived growth factor (PDGF): Promote epithelial cell growth and tissue remodeling in the gut.

Vascular Endothelial Growth Factor (VEGF): Stimulates blood vessel formation, supporting nutrient delivery and gut maturation.

9) Hormones: Insulin, glucagon, estrogen, growth hormone etc. are present in trace amounts.

Feed Additives

Improve feed utilization and growth in calves. Common additives in calf nutrition are, antibiotics, probiotics, prebiotics and acidifiers.

1. Antibiotics

Antibiotics are added in milk replacers and calf starter.

Commonly used Ionophore: Aureomycin, Monensin etc.

Non-ionophore: Flavomycin, Virginiamycin etc.

Antibiotics suppress the undesired toxin producing microorganisms that utilize nutrients meant for the host and hence, improving nutrient utilization, feed conversion ratio and growth rate. Many countries have banned use of antibiotic growth promoters due to risk of antibiotic resistance.

2. Probiotics

Monoculture or mixed culture of live micro-organisms is added to calf feed in adequate amounts and provides health benefits to the host. It protects against digestive disorders, improves feed efficiency and growth rate.

Mechanism of action: Lowers the gut pH, compete with pathogens for nutrients, inhibit pathogen adhesion, stimulate immune system, produce antimicrobial peptides e.g. lactobacillus species produce nisin, lactobrevin, acidophilin etc. in the lumen of GIT.

Common genera used as probiotics in calves are Lactobacillus, Lactococcus, Enterococcus, Streptococcus, Bifidobacterium, Bacillus and Saccharomyces.

3. Prebiotics

Prebiotics are substrates, undigested by the host but are selectively used by gut microorganisms, providing health benefit to the host. e.g. Mannan oligosaccharides (MOS), Xylan oligosaccharides (XOS), Fructooligosaccharides (FOS), Galactooligosaccharides (GOS), β-glucans (from yeast, fungi, and cereal grains) and lactulose (disaccharide containing galactose and fructose).

Mechanism of action: Selective stimulation of beneficial bacteria, bind to pathogens (e.g. E. coli) and void them with feces, activate immune cells receptor, increase production of short chain fatty acids (SCFAs) which stimulate production of secretory IgA in intestine and epithelial development in rumen as well as lower gut.

4. Acidifiers

Acidifiers such as formic acid, lactic acid, Glucono-delta-lactone (GLA) etc. are added to calf feed and milk replacer. Acidifiers improve digestion especially of soya/plant-based milk replacer by aiding in lowering abomasa pH. Plant based milk replacer does not clot in abomasum unlike dam’s milk. Acidifiers also help in lowering rumen pH when added to solid feed.

Conclusion

Extensive research has been conducted in calf nutrition, yet new areas are being explored such as role of milk bioactive compounds. Butyric acid and oligosaccharides from dam’s milk have positive role in calf gut health. Different microbial species are being explored as potential probiotic and some has very good effect on growth. Antimicrobial peptides such as lactoferrin improves growth performance in calf. Alternative feed additives hold potential for promoting environmentally sustainable calf rearing.