Extruded fat pellets for pelleted calf starter

High-fat extruded pellets appear to have some economic limitations.

March 22, 2023

7 Min Read

By A.F.  Kertz, PhD, PAS, DIPL ACAN

It seems intuitive that adding fat to a calf starter would increase energy intake and calf performance.   But I learned more than 25 years ago from reviewing literature that the results were generally negative (Kertz 2013) for adding fat to calf starters.  A good example is the classic study by Kuehn et al. (1994) in which calf starters were fed with either 0 or 17.1% ground, roasted soybeans resulting in starters with either 3.7 % or 7.3% total fat.  The added fat decreased intake and performance both before weaning at 42 days of age and after up to 56 days of age.  A study in 2015 (Hill et al.; Kertz 2016) found that adding tallow or soy oil reduced intake and daily gain more so with soy oil than with tallow (see my book pages 77 to 82, Kertz 2019).  So why would adding fat to calf starters be negative?  I think it is because there is no resident protozoa population yet in the calf rumen.  This results in pH in the mid to low 5.0 range (see my book pages 73 to 77).   Jeff Firkins at The Ohio State University (personal correspondence 2019) commented to me that protozoa consume lactate and store glycogen rather than ferment the glucose.  Dietary unsaturated fatty acids also defaunate (kill) protozoa.  This is most likely why preweaned calves have low rumen pH.

In 2018, Berends et al. fed a high fat (~37%) extruded pellet in a range of levels mixed with a pelleted calf starter and straw.  This study was with female Holstein calves ai one large dairy herd in Spain.  There were no differences among treatments in intake and only a significant difference in daily gain between two treatments.  But there were no negative effects.  Why not?

That led to another more recent study (Amado et al., 2022) at the Trouw Calf & Beef Research Unit in the Netherlands.  Sixty Holstein bull calves (100.6 ± 1.9 lb body weight, 2.5 ± 0.5 days of age) were sourced from local dairy farms within 14 km from the calf facility.  Calves had been fed 3 L colostrum within 3 hours of birth followed by 2 feedings of 2 L for a total of 3 feedings of colostrum within the first 24 hours of life.   Blood was sampled upon arrival at the facility within 48 to 72 hours after birth.  Calves were then assigned to 1 of 20 blocks (3 calves per block) based on IgG categories (low: 1000 to 2000 mg/dL; high > 2000 mg/dL), day of arrival, and body weight (BW).  Within each block, calves were randomly assigned to solid feed treatments: 1) calf starter control pellet (Control 3.1% fat); 2) control pellet mixed with an extruded pellet with hydrogenated palm free fatty acids (PFA) 7.1% fat in pellet mix; and 3) control pellet mixed with extruded pellet with hydrogenated rapeseed triglycerides (RFT 6.7% fat in pellet mix). 

The Control pelleted starter (Table 1) was relatively low in starch at 21% whereas the extruded pellets had around 40% starch to absorb their high fat content.  Palmitic and stearic fatty acid levels in extruded pellets reflected their respective fat sources.  The high melting point of the rapeseed triglyceride in the extruded pellet will show up later in this discussion.

kertz march 1.jpg

Calves were housed indoors in individual pens with 50% rubber-slatted floors in the front and 50% lying area in the back with a mattress covered with flax straw.  From arrival to 14 days of age, calves were fed 6 L of a 22.8 % CP and 18.4% fat (DM basis) milk replacer mixed to 15% solids which was fed twice daily at 3 L per feeding at 0700 and 1700 hours.  Milk replacer fed was then increased to 3.5 L from 15 to 42 days of age, after which it was decreased to 2 L until full weaning at 49 days of age.  Two post weaned periods followed from 50 to 84 days and 85 to 112 days.  Calves had free access to water, starter pellets, and wheat straw (4.2% CP, 71.8 % NDF, 50.6% ADF DM basis and with 3-7 cm chop length) with each component provided in separate buckets.  For each extruded treatment, a mix of 90% pelleted starter and 10% extruded pellets was fed with the TG mix being 18% CP, 6.7% ether extract, and 22.7% starch; and the FA mix being 17.9% CP, 7.1% ether extract, and 23.3% starch.  

A separate set of 24 weaned Holstein bull calves were fed the same as above and used for digestion trials.  Calves were adapted for 14 days prior to being subjected to  a 72-hour total collection period.

Kertz March 2.jpg


Key points are:

  • Milk replacer intake was similar at about 2 lb across treatments (not shown).

  • Starter intake was similar preweaning (0 to 49 days) and approached difference (P

  • Daily gains did not differ for preweaning period (days 0 to 49).  But during 50 to 84 days (P

  • Dry matter and organic matter digestibilities were greater (P

  • Crude fat digestibility was greater (P

There are several significant caveats to this study and results:

  • The study was done with Holstein dairy bull calves.  For the first 2 months, that is not an issue as long as initial body weight is used as a covariate (adjusts to the fact that bull calves weigh more than heifer calves):  On average, male Holstein calves at birth weighed 7 % more than female calves (Kertz et al., 1998).

  • All the differences in this study are postweaning.  That is when bull calves would really begin to pull away from heifer calves in performance.

  • Extrusion disperses fat in the highly gelatinized starch in the pellet.  This minimizes greasy palatability factors on intake and negative rumen effects primarily due to unsaturated fatty acids.  Thus, the palm fatty acid treatment had the most neutral effect on rumen function and intake and performance.

  • The cost of extrusion likely makes this economically infeasible for inclusion in calf starters.

The Bottom Line

While there were some positive effects for using a free fatty acid versus triglyceride fat source in a high fat extruded pellet mixed with a pelleted starter and straw, there was no benefit until after weaning at 49 days of age.  Such a high fat extruded pellet would also likely be quite uneconomical.



 Amado, L., L. N. Leal, H. van Laar, H. Berends, W. J. J. Gerrits, and J. Martin-Tereso. 2022. Effects of mixing a high-fat extruded pellet with a dairy calf starter on performance, feed intake, and digestibility.  J. Dairy Sci. 105:8087-8098.

Berends, H., M. Vidal, M. Terré, L. N. Leal, J. Martín-Tereso, and A. Bach. 2018. Effects of fat inclusion in starter feeds for dairy calves by mixing increasing levels of a high-fat extruded pellet with a conventional highly fermentable pellet. J. Dairy Sci. 101:10962– 10972.

Hill, T.M., H.G. Bateman II, J.M. Aldrich, J.D. Quigley, R.L. Schlotterbeck.  2015.  Inclusion of tallow and soybean oil to calf starters fed to dairy calves from birth to four months of age on calf performance and digestion.  J. Dairy Sci.  98:4882-4888.

Kertz, A. F., L. F. Reutzel, B. A. Barton, and R. L. Ely.  1997.  Body weight, body condition score, and wither height of prepartum Holstein cows and body weight and sex of calves by parity.  A database and summary.  J. Dairy Sci.  80:525-529.

Kertz, A. F.  2013. Addition of fat to calf starters not beneficial. Feedstuffs. January 14, p. 12-13

Kertz, A. F.  2016. Tallow, soybean oil in calf starters reduce performance Feedstuffs, January 25 p. 36-38

Kertz, A. F.  Dairy Calf and Heifer Feeding and Management—Some Key Concepts and  Practices.  Outskirts Press, July 31, 2019, 166 pages. https://outskirtspress.com/dairycalfandheiferfeedingandmanagement

Kuehn, C. S., D. E. Otterby, J. G. Linn, W. G Olson, H. Chester-Jones, G. D. Marx, and J. A. Barmore.  1994.  The effect of dietary energy concentration on calf performance.  J. Dairy Sci. 77:2621-2629.



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