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In the evolving U.S. dairy industry, fewer cows are producing greater volumes of milk per cow than in previous decades. Jersey and Holstein cows, two of the most popular dairy breeds, differ in their impacts on milk production, farm sustainability, and environmental footprint. Each breed is unique with different production and excretion patterns requiring different dietary nutrient intakes. In the previous 20 years, dietary alfalfa (ALF) has been gradually replaced with corn silage (CS) in the diets of lactating dairy cows and the effects of this switch on excretion and production are not fully understood. Two studies were conducted to determine the effects of replacing ALF with CS on lactation performance, N efficiency (NEFF), and N excretions and the difference between Jersey and Holstein cows on lactation performance, feed efficiency (FE), and NPK excretions.
The first study was a meta-analysis examining the effects of replacing ALF with CS on lactation performance, NEFF, and nitrogen excretion (NMANURE). Data from 193 studies (698 treatment means) published between 2018 to 2023 were analyzed using multiple models developed using a backward stepwise approach. Our findings indicate that nutrient intakes from both CS and ALF significantly influenced milk yield (MY) and energy-corrected milk yield (ECM), with ALF generally having a negative effect on production. The NEFF was also affected by nutrient intakes from both CS and ALF. Increased protein intake negatively affected NEFF, and a higher rumen degradable protein intake (RDPI) from ALF was associated with increased MUN. However, no significant effect of protein intake from CS on milk urea nitrogen (MUN) was observed. Additionally, increases in dry matter intake (DMI) and RDPI, regardless of forage source (CS or ALF), led to higher NMANURE. These findings suggest that both ALF and CS can be strategically utilized in targeted nutrient and waste management strategies. The second study investigated the effects of breed on MY and milk components, ECM, NEFF, FE, and manure excretions of N, P, and K in an automatic milking system (AMS). In this study, 28 Jersey and 23 Holstein cows of mixed parity and between 70 and 280 days in milk were used. The study consisted of 6 periods of 14 days each with samples collected from day 3 to day 7 of each period. Cows were fed a partial mixed ration (PMR) at the feed bunk and pellets at the AMS. The pellets contained Titanium dioxide (TiO2) as an internal marker to estimate total fecal production and DMI. Milk samples were taken once per period and analyzed for milk fat, protein, lactose, and MUN, while body weights (BW) were recorded during each AMS visit. Fecal grab samples were collected and analyzed for indigestible neutral detergent fiber (iNDF), N, P, K, and Ti. Holstein cows produced more milk, milk protein, and ECM but less milk fat than Jersey cows. Jersey cows showed a greater FE (1.21 vs 1.03) and income over feed costs (IOFC of $6.47 vs $3.51 per cow per day) than Holstein cows. Holsteins had greater DMI and total fecal excretion, however, Jersey cows had greater DMI and excretions per kg BW. These breed-related differences in production efficiencies and nutrient excretion have significant implications for the sustainability and economics of dairy farms.
